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  • 1. Plant anatomyFrom Wikipedia, the free encyclopediaPlant anatomy or phytotomy is the general term for the study of the internal structure ofplants. While originally it included plant morphology, which is the description of thephysical form and external structure of plants, since the mid Twentieth Century theinvestigation of plant anatomy is considered a separate, distinct field, and refers to justthe internal plant structures.[1] Plant anatomy is now frequently investigated at the cellularlevel, and often involves the sectioning of tissues and microscopy.Contents • 1 Structural divisions • 2 History • 3 See also • 4 References • 5 External linksStructural divisionsPlant anatomy is sometimes divided into the following categories: Flower anatomy Calyx Corolla Androecium Gynoecium Leaf anatomy Leaf anatomy Stem anatomy Stem structure Fruit/Seed anatomy Ovule Seed structure Pericarp Accessory fruit Wood anatomy Bark Cork Phloem Vascular cambium Heartwood and sapwood branch collar Root anatomy Root structureHistoryAbout 300 BCE Theophrastus wrote a number of plant treatises, only two of whichsurvive. He developed concepts of plant morphology and classification, which did notwithstand the scientific scrutiny of the Renaissance.Plant anatomy, From Wikipedia, the free encyclopedia 1
  • 2. A Swiss physician and botanist, Gaspard Bauhin, introduced binomial nomenclature intoplant taxonomy. He published Pinax theatri botanici in 1596, which was the first to usethis convention for naming of species. His criteria for classification included naturalrelationships, or affinities, which in many cases were structural.Italian doctor and microscopist, Marcello Malpighi, was one of the two founders of plantanatomy. In 1671 he published his Anatomia Plantarum, the first major advance in plantphysiogamy since Aristotle.The British doctor, Nehemiah Grew was one of the two founders of plant anatomy. Hepublished An Idea of a Philosophical History of Plants in 1672 and The Anatomy ofPlants in 1682. Grew is credited with the recognition of plant cells, although he calledthem vesicles and bladders. He correctly identified and described the sexual organs ofplants (flowers) and their parts.In the Eighteenth Century, Carolus Linnaeus established taxonomy based on structure,and his early work was with plant anatomy. While the exact structural level which is tobe considered to be scientifically valid for comparison and differentiation has changedwith the growth of knowledge, the basic principles were established by Linnaeus. Hepublished his master work, Species Plantarum in 1753.In 1802, French botanist, Charles-François Brisseau de Mirbel, published Traitédanatomie et de physiologie végétale (Treatise on Plant Anatomy and Physiology)establishing the beginnings of the science of plant cytology.In 1812, Johann Jacob Paul Moldenhawer published Beyträge zur Anatomie der Pflanzen,describing microscopic studies of plant tissues.In 1813 a Swiss botanist, Augustin Pyrame de Candolle, published Théorie élémentairede la botanique, in which he argued that plant anatomy, not physiology, ought to be thesole basis for plant classification. Using a scientific basis, he established structuralcriteria for defining and separating plant genera.In 1830, Franz Meyen published Phytotomie, the first comprehensive review of plantanatomy.In 1838 German botanist, Matthias Jakob Schleiden, published Contributions toPhytogenesis, stating, "the lower plants all consist of one cell, while the higher plants arecomposed of (many) individual cells" thus confirming and continuing Mirabels work.A German-Polish botanist, Eduard Strasburger, described the mitotic process in plantcells and further demonstrated that new cell nuclei can only arise from the division ofother pre-existing nuclei. His Studien über Protoplasma was published in 1876.Gottlieb Haberlandt, a German botanist, studied plant physiology and classified planttissue based upon function. On this basis, in 1884 he published PhysiologischePflanzenanatomie (Physiological Plant Anatomy) in which he described twelve types oftissue systems (absorptive, mechanical, photosynthetic, etc.).British paleobotanists Dunkinfield Henry Scott and William Crawford Williamsondescribed the structures of fossilized plants at the end of the Nineteenth Century. ScottsStudies in Fossil Botany was published in 1900.Following Charles Darwins Origin of Species a Canadian botanist, Edward CharlesJeffrey, who was studying the comparative anatomy and phylogeny of different vascularplant groups, applied the theory to plants using the form and structure of plants toestablish a number of evolutionary lines. He published his The Anatomy of Woody Plantsin 1917.Plant anatomy, From Wikipedia, the free encyclopedia 2
  • 3. The growth of comparative plant anatomy was spearheaded by a British botanist, AgnesArber. She published Water Plants: A Study of Aquatic Angiosperms in 1920,Monocotyledons: A Morphological Study in 1925, and The Gramineae: A Study ofCereal, Bamboo and Grass in 1934.Following World War II, Katherine Esau published, Plant Anatomy (1953), whichbecame the definitive textbook on plant structure in North American universities andelsewhere, it was still in print as of 2006. She followed up with her Anatomy of seedplants in 1960.See also • Plant morphology • Plant physiologyReferences 1. ^ Raven, P. H., R. F. Evert, & S. E. Eichhorn. Biology of Plants, 7th ed., page 9. (New York: W. H. Freeman, 2005). ISBN 0-7167-1007-2. • Eames, Arthur Johnson and MacDaniels, Laurence H. (1947) An Introduction to Plant Anatomy McGraw-Hill, New York; • Esau, Katherine (1965) Plant Anatomy (2nd ed.) Wiley, New York;External links • Farabee, M.J. (2001) "Plants and their structure" Estrella Mountain Community College, Phoenix, Arizona • Botanical Visual GlossaryPlant morphologyPlant morphology (or phytomorphology) is the general term for the study of themorphology (physical form and external structure) of plants.[1] This is usually considereddistinct from plant anatomy, which is the study of the internal structure of plants,especially at the microscopic level. Plant morphology is useful in the identification ofplants.Inflorescences emerging from protective coveringsPlant anatomy, From Wikipedia, the free encyclopedia 3
  • 4. Contents • 1 Scope • 2 A comparative science o 2.1 Homology o 2.2 Convergence • 3 Vegetative and reproductive characters o 3.1 Use in identification o 3.2 Alternation of generations • 4 Plant development o 4.1 Plant growth o 4.2 Morphological variation 4.2.1 Positional effects 4.2.2 Environmental effects 4.2.3 Juvenility • 5 See also • 6 References • 7 External linksScopePlant morphology "represents a study of the development, form, and structure of plants,and, by implication, an attempt to interpret these on the basis of similarity of plan andorigin."[2] There are four major areas of investigation in plant morphology, and eachoverlaps with another field of the biological sciences.First of all, morphology is comparative, meaning that the morphologist examinesstructures in many different plants of the same or different species, then drawscomparisons and formulates ideas about similarities. When structures in different speciesare believed to exist and develop as a result of common, inherited genetic pathways,those structures are termed homologous. For example, the leaves of pine, oak, andcabbage all look very different, but share certain basic structures and arrangement ofparts. The homology of leaves is an easy conclusion to make. The plant morphologistgoes further, and discovers that the spines of cactus also share the same basic structureand development as leaves in other plants, and therefore cactus spines are homologous toleaves as well. This aspect of plant morphology overlaps with the study of plant evolutionand paleobotany.Asclepia syriaca showing complex morphology of the flowers.Secondly, plant morphology observes both the vegetative (somatic) structures of plants,as well as the reproductive structures. The vegetative structures of vascular plantsincludes the study of the shoot system, composed of stems and leaves, as well as the rootPlant anatomy, From Wikipedia, the free encyclopedia 4
  • 5. system. The reproductive structures are more varied, and are usually specific to aparticular group of plants, such as flowers and seeds, fern sori, and moss capsules. Thedetailed study of reproductive structures in plants led to the discovery of the alternationof generations found in all plants and most algae. This area of plant morphology overlapswith the study of biodiversity and plant systematics.Thirdly, plant morphology studies plant structure at a range of scales. At the smallestscales are ultrastructure, the general structural features of cells visible only with the aidof an electron microscope, and cytology, the study of cells using optical microscopy. Atthis scale, plant morphology overlaps with plant anatomy as a field of study. At thelargest scale is the study of plant growth habit, the overall architecture of a plant. Thepattern of branching in a tree will vary from species to species, as will the appearance ofa plant as a tree, herb, or grass.Fourthly, plant morphology examines the pattern of development, the process by whichstructures originate and mature as a plant grows. While animals produce all the bodyparts they will ever have from early in their life, plants constantly produce new tissuesand structures throughout their life. A living plant always has embryonic tissues. The wayin which new structures mature as they are produced may be affected by the point in theplants life when they begin to develop, as well as by the environment to which thestructures are exposed. A morphologist studies this process, the causes, and its result.This area of plant morphology overlaps with plant physiology and ecology.A comparative scienceA plant morphologist makes comparisons between structures in many different plants ofthe same or different species. Making such comparisons between similar structures indifferent plants tackles the question of why the structures are similar. It is quite likely thatsimilar underlying causes of genetics, physiology, or response to the environment haveled to this similarity in appearance. The result of scientific investigation into these causescan lead to one of two insights into the underlying biology: 1. Homology - the structure is similar between the two species because of shared ancestry and common genetics. 2. Convergence - the structure is similar between the two species because of independent adaptation to common environmental pressures.Understanding which characteristics and structures belong to each type is an importantpart of understanding plant evolution. The evolutionary biologist relies on the plantmorphologist to interpret structures, and in turn provides phylogenies of plantrelationships that may lead to new morphological insights.Homology Main article: Homology (biology)When structures in different species are believed to exist and develop as a result ofcommon, inherited genetic pathways, those structures are termed homologous. Forexample, the leaves of pine, oak, and cabbage all look very different, but share certainbasic structures and arrangement of parts. The homology of leaves is an easy conclusionto make. The plant morphologist goes further, and discovers that the spines of cactus alsoshare the same basic structure and development as leaves in other plants, and thereforecactus spines are homologous to leaves as well.Convergence Main article: Convergent evolutionPlant anatomy, From Wikipedia, the free encyclopedia 5
  • 6. When structures in different species are believed to exist and develop as a result ofcommon adaptive responses to environmental pressure, those structures are termedconvergent. For example, the fronds of Bryopsis plumosa and stems of Asparagussetaceus both have the same feathery branching appearance, even though one is an algaand one is a flowering plant. The similarity in overall structure occurs independently as aresult of convergence. The growth form of many cacti and species of Euphorbia is verysimilar, even though they belong to widely distant families. The similarity results fromcommon solutions to the problem of surviving in a hot, dry environment.Euphorbia obesa, a spurgeAstrophytum asterias, a cactus.Vegetative and reproductive charactersPlant morphology treats both the vegetative structures of plants, as well as thereproductive structures.The vegetative (somatic) structures of vascular plants include two major organ systems:(1) a shoot system, composed of stems and leaves, and (2) a root system. These twosystems are common to nearly all vascular plants, and provide a unifying theme for thestudy of plant morphology.By contrast, the reproductive structures are varied, and are usually specific to aparticular group of plants. Structures such as flowers and fruits are only found in theangiosperms; sori are only found in ferns; and seed cones are only found in conifers andother gymnosperms. Reproductive characters are therefore regarded as more useful forthe classification of plants than vegetative characters.Use in identification Main article: Identification keyPlant biologists use morphological characters of plants which can be compared, measuredcounted and described to assess the differences or similarities in plant taxa and use thesecharacters for plant identification, classification and descriptions.When characters are used in descriptions or for identification they are called diagnosticor key characters which can be either qualitative and quantitative. 1. Quantitative characters are morphological features that can be counted or measured for example a plant species has flower petals 10-12 mm wide. 2. Qualitative characters are morphological features such as leaf shape, flower color or pubescence.Both kinds of characters can be very useful for the identification of plants.Alternation of generations Main article: Alternation of generationsThe detailed study of reproductive structures in plants led to the discovery of thealternation of generations, found in all plants and most algae, by the German botanistWilhelm Hofmeister. This discovery is one of the most important made in all of plantPlant anatomy, From Wikipedia, the free encyclopedia 6
  • 7. morphology, since it provides a common basis for understanding the life cycle of allplants.Plant developmentProgressive sections of a stem, showing internal development and growth.[3]Plant development is the process by which structures originate and mature as a plantgrows. It is a subject studies in plant anatomy and plant physiology as well as plantmorphology.The process of development in plants is fundamentally different from that seen invertebrate animals. When an animal embryo begins to develop, it will very early produceall of the body parts that will ever have in its life. When the animal is born. or hatchesfrom its egg. it has all its body parts and from that point will only grow larger and moremature. By contrast, plants constantly produce new tissues and structures throughout theirlife from meristems located at the tips of organs, or between mature tissues. Thus, aliving plant always has embryonic tissues.The properties of organization seen in a plant are emergent properties which are morethan the sum of the individual parts. "The assembly of these tissues and functions into anintegrated multicellular organism yields not only the characteristics of the separate partsand processes but also quite a new set of characteristics which would not have beenpredictable on the basis of examination of the separate parts."[4] In other words, knowingeverything about the molecules in a plant are not enough to predict characteristics of thecells; and knowing all the properties of the cells will not predict all the properties of aplants structure.Plant growth Further information: Meristem, Cellular differentiation, Morphogenesis, and Plant embryogenesisA vascular plant begins from a single celled zygote, formed by fertilisation of an egg cellby a sperm cell. From that point, it begins to divide to form a plant embryo through theprocess of embryogenesis. As this happens, the resulting cells will organize so that oneend becomes the first root, while the other end forms the tip of the shoot. In seed plants,Plant anatomy, From Wikipedia, the free encyclopedia 7
  • 8. the embryo will develop one or more "seed leaves" (cotyledons). By the end ofembryogenesis, the young plant will have all the parts necessary to begin in its life.Once the embryo germinates from its seed or parent plant, it begins to produce additionalorgans (leaves, stems, and roots) through the process of organogenesis. New roots growfrom root meristems located at the tip of the root, and new stems and leaves grow fromshoot meristems located at the tip of the shoot. Branching occurs when small clumps ofcells left behind by the meristem, and which have not yet undergone cellulardifferentiation to form a specialized tissue, begin to grow as the tip of a new root orshoot. Growth from any such meristem at the tip of a root or shoot is termed primarygrowth and results in the lengthening of that root or shoot. Secondary growth results inwidening of a root or shoot from divisions of cells in a cambium.In addition to growth by cell division, a plant may grow through cell elongation. Thisoccurs when individual cells or groups of cells grow longer. Not all plant cells will growto the same length. When cells on one side of a stem grow longer and faster than cells onthe other side, the stem will bend to the side of the slower growing cells as a result.Morphological variationPlants exhibit natural variation in their form and structure. While all organisms vary fromindividual to individual, plants exhibit an additional type of variation. Within a singleindividual, parts are repeated which may differ in form and structure from other similarparts. This variation is most easily seen in the leaves of a plant, though other organs suchas stems and flowers may show similar variation. There are three primary causes of thisvariation: positional effects, environmental effects, and juvenility.Positional effectsVariation in leaves from the giant ragweed illustrating positional effects. The lobedleaves come from the base of the plant, while the unlobed leaves come from the top of theplant.Although plants produce numerous copies of the same organ during their lives, not allcopies of a particular organ will be identical. There is variation among the parts of amature plant resulting from the relative position where the organ is produced. Forexample, along a new branch the leaves may vary in a consistent pattern along thebranch. The form of leaves produced near the base of the branch will differ from leavesproduced at the tip of the plant, and this difference is consistent from branch to branch ona given plant and in a given species. This difference persists after the leaves at both endsof the branch have matured, and is not the result of some leaves being younger thanothers.Environmental effectsThe way in which new structures mature as they are produced may be affected by thepoint in the plants life when they begin to develop, as well as by the environment towhich the structures are exposed. This can be seen in aquatic plants and emergent plants.Plant anatomy, From Wikipedia, the free encyclopedia 8
  • 9. JuvenilityJuvenility in a seedling of European beech. Notice the difference in shape between thefirst dark green "seed leaves and the lighter second pair of leaves.The organs and tissues produced by a young plant, such as a seedling, are often differentfrom those that produced by the same plant when it is older. This phenomenon is knownas juvenility. For example, young trees will produce longer, leaner branches that growupwards more than the branches they will produce as a fully grown tree. In addition,leaves produced during early growth tend to be larger, thinner, and more irregular thanleaves on the adult plant. Species of juvenile plants may look so completely differentfrom the adult leaves that egg-laying insects do not recognize the plant as food for theiryoung.See also • List of plant morphology terms • Plant anatomy • Plant physiology • Plant evolutionary developmental biologyReferences 1. ^ Raven, P. H., R. F. Evert, & S. E. Eichhorn. Biology of Plants, 7th ed., page 9. (New York: W. H. Freeman, 2005). ISBN 0-7167-1007-2. 2. ^ Harold C. Bold, C. J. Alexopoulos, and T. Delevoryas. Morphology of Plants and Fungi, 5th ed., page 3. (New York: Harper-Collins, 1987). ISBN 0-06-040838-1. 3. ^ Winterborne J, 2005. Hydroponics - Indoor Horticulture [1] 4. ^ Leopold, A. C. Plant Growth and Development, page 183. (New York: McGraw-Hill, 1964).External links • Botanical Visual GlossaryPlant anatomy, From Wikipedia, the free encyclopedia 9
  • 10. List of plant morphology termsJump to: navigation, search It has been suggested that Glossary of botanical terms be merged into this article or section. (Discuss)Biologists that study plant morphology use a number of different terms to describe plantorgans and parts that can be observed with the human eye using no more than a hand heldmagnifying lens. These terms are used to identify and classify plants.Contents1 General plant terms o 1.1 Plant habit o 1.2 Duration • 2 Vegetative morphology o 2.1 Roots o 2.2 Stems o 2.3 Buds o 2.4 Leaves • 3 Epidermis and periderm texture • 4 Floral morphology o 4.1 Basic flower parts o 4.2 Inflorescences o 4.3 Insertion of floral parts • 5 Specialized terms o 5.1 Union of flower parts o 5.2 Flower sexuality and presence of floral parts o 5.3 Flower symmetry • 6 Pollination and fertilization o 6.1 Embryo development • 7 Fruits and seeds o 7.1 Terms for fruits o 7.2 Fruit types • 8 Seedless reproduction o 8.1 Pteridophyte sporangium terms o 8.2 Bryophyte gametangium terms o 8.3 Bryophyte sporangium terms • 9 See also • 10 ReferencesGeneral plant terms • Abaxial - located on the side away from the axis. • Wing - any flat surfaced structure emerging from the side or summit of an organ; seeds, stems.Plant habit • Acaulescent - the leaves and inflorescence rise from the ground, appearing to have no stem.Plant anatomy, From Wikipedia, the free encyclopedia 10
  • 11. • Acid plant - plants with acid saps, normally due to the production of ammonium salts (malic and oxalic acid) • Acme - the period when the plant or population is at its maximum vigor. • Actinomorphic - parts of plants that are radially symmetrical in arrangement. • Arborescent - growing into a tree-like habit, normally with a single woody stem. • Ascending - growing uprightly, in an upward direction, heading in the direction of the top. • Assurgent - growth ascending. • Branching - dividing into multiple smaller segments. • Caducous - falling away early. • Caulescent - with a well developed stem above ground. • Cespitose - forming dense tufts, normally applied to small plants typically growing into mats, tufts or clumps. • Creeping - growing along the ground and producing roots at intervals along surface. • Deciduous - falling away after its function is completed. • Decumbent - growth starts off prostrate and the ends become upright. • Deflexed - bending downward. • Determinate growth - Growing for a limited time, floral formation and leaves. • Dimorphic - of two different forms. • Ecad - a plant assumed to be adapted to a specific habitat. • Ecotone - the boundary that separates two plant communities, generally of major rank - trees in woods and grasses in savanna for example. • Ectogenesis - variation in plants due to conditions out side of the plants. • Ectoparasite - a parasitic plant that has most of its mass outside of the host, the body and reproductive organs of the plant lives outside of the host. • Epigeal - living on the surface of the ground. See also terms for seeds. o Epigean - occurring on the ground. o Epigeic - plants with stolons on the surface of the ground. o Epigeous - on the ground. Used for leaf fungus that live on the surface of the leaf. • Epilithic - growing on the surface of rocks. • Epiphloedal - growing on the bark of trees. o Epiphloedic - an organism that grows on the bark of trees. • Epiphyllous - growing on the leaves. For example, Helwingia japonica has epiphyllous flowers (ones that form on the leaves).[1] • Epiphyte - growing on another organism but not parasitic. Not growing on the ground. o Epiphytic - having the nature of an epiphyte. • Equinoctial - a plants that has flowers that open and close at definite times during the day. • Erect - having an essentially upright vertical habit or position. • Escape - plant originally under cultivation that has become wild, garden plant growing in natural areas. • Evergreen - remaining green in the winter or during the normal dormancy period for other plants.Plant anatomy, From Wikipedia, the free encyclopedia 11
  • 12. • Eupotamous - living in rivers and streams. • Euryhaline - normally living in salt water but tolerant of variable salinity rates. • Eurythermous - tolerant of a wide range of temperature. • Exclusive species - confined to specific location. • Exotic - not native to the area or region. • Exsiccatus - a dried plant, most often used for specimens in a herbarium. • Lax - non upright, growth not strictly upright or hangs down from the point of origin. • Parasitic - using another plant as a source of nourishment. • Precocious - flowering before the leaves emerge. • Procumbent - growing prostrate or trailing but not rooting at the nodes. • Prostrate - laying flat on the ground, stems or even flowers in some species. • Repent - creeping. • Rosette - cluster of leaves with very short internodes that are crowded together, normally on the soil surface but sometimes higher on the stem. o Rostellate - like a rosette. o Rosulate - arranged into a rosette. • Runner - an elongated, slender branch that roots at the nodes or tip. • Stolon - A branch that forms near the base of the plant and grows horizontally and roots and produces new plants at the nodes or apex. o Stoloniferous - plants produce stolons. • Semi-erect - • Suffrutescent - somewhat shrubby, or shrubby at the base. • Upright - • Virgate - wand-like, slender erect growing stem with many leaves or very short branches. • Woody - forming secondary growth laterally around the plant so as to form wood.DurationDuration of individual plant lives are described using these terms: • Annual - plants that live, reproduce and die in one growing season. • Biennial - plants that need two growing seasons to complete their life cycle, normally vegetative growth the first year and flowering the second year. • Herbs - see herbaceous. • Herbaceous - plants with shoot systems that die back to ground each year- both annual and non-woody perennial plants. • Herbaceous perennial - non-woody plants that live for more than two years and the shoot system dies back to the soil level each year. • Woody perennial - true shrubs and trees or some vines with shoot systems that remain alive above the soil surface from one year to the next. • Monocarpic - plants that live for a number of years then after flowering and seed set die.Vegetative morphology • Vernation - the arrangement of leaves, petals or sepals in an unopened bud.Plant anatomy, From Wikipedia, the free encyclopedia 12
  • 13. RootsRoots generally do not offer many characters used in plant identification andclassification but are important in determining plant duration though in some groups theyvery important for proper identification including the grasses. • Adventitious - roots that form from other than the hypocotyl or from another roots. Roots forming on the stem are adventitious. • Aerial - roots growing in the air. • Crown - the place where the roots and stem meet, which may or may not be clearly visible.[2] • Fibrous - roots are thread-like and normally tough. • Fleshy - roots are relatively thick and soft, normally made up of storage tissue. Roots are typical long and thick but not thickly rounded in shape. • Haustorial - specialized roots that invade other plants and absorb nutrients from those plants. • Lignotuber - root tissue that allows plants to regenerate after fire or other damage. • Primary - roots that develops from the radically of the embryo, normally the first root to emerge from the seed as it germinates. • Root Hairs - very small, often one cell wide, roots that do most of the water and nutrient absorption. • Secondary - roots forming off of the primary root, often called branch roots. • Tap - a primary root that more or less enlarges and grows downward into the soil. • Tuberous - roots that are thick and soft, with storage tissue. Typically thick round in shape.Stems • Accessory buds - • Acrocarpous - produced at the end of a branch. • Acutangular - a stem that has several longitudinally running ridges with sharp edges. • Adventitious buds - • Alternate - buds are staggered on opposite sides of the branch • Accessory buds - • Bark - the outer layers of woody plants; cork, phloem, and vascular cambium. • Branches - • Bud - an immature stem tip, typically an embryonic shoot, ether producing a stem, leaves or flowers. • Bulb - an underground stem normally with a short basal surface and with thick fleshy leaves. • Bundle scar - • Caudex - the hard base produced by herbaceous perennials used to overwinter the plant. • Caulescent - with a distinctive stem. • Cladode - • Cladophyll - a flattened stem that is leaf-like and green- used for photosynthesis, normally plants have no or greatly reduced leaves. • Climbing - typically long stems, that cling to other objects.Plant anatomy, From Wikipedia, the free encyclopedia 13
  • 14. • Corm - a compact, upright orientated stem that is bulb-like with hard or fleshy texture and normally covered with papery, thin dry leaves. Most often produced under the soil surface. • Cuticle - a waxy membrane covering some leaves and roots that is water-tight. • Decumbent - stems that lay on the ground but have the ends turning upward. • Dormant - a state of no growth or reduced growth • Early wood - • Epidermis - a layer of cells that cover all primary tissue separating them from the outside environment. • Erect - growing upright. • Flower bud - • Fruticose - woody stemmed with a shrub-like habit. Branching near the soil with woody based stems. • Guard cell - • Herbaceous - non-woody and dying to the ground at the end of the growing season. Annual plants die, while perennials regrow from from parts on the soil surface or below ground the next growing season. • Heartwood - • Latent buds - • Lenticel - • Internode - spaces between the nodes. • Late wood - • Lateral bud - • Leaf axils - the space created between a leaf and its branch. This is especially pronounced on monocots like bromeliads. • Leaf bud - • Leaf scar - the mark left on a branch from the previous location of a bud or leaf. • Lenticels - lens-shaped or warty patches of parenchymatous tissue on the surface of the stem. • Node - were leaves and buds are attached to the stem. • Pith - the spongy tissue at the center of a stem. o Chambered pith - o Continuous pith - o Diaphragmed pith - • Spine - an adapted leaf that is usually hard and sharp and is used for protection, and occasionally shading of the plant • Prickle - an extension of the cortex and epidermis that ends with a sharp point. • Prostrate - growing flat on the soil surface. • Rhizome - A horizontally orientated, prostrate stem with reduced scale-like leaves, normally growing under ground but also at the soil surface. Also produced by some species that grow in trees or water. • Rootstock - the underground part of a plant normally referring to a caudex or rhizome. • Runner - an above ground stem usually rooting and producing new plants at the nodes. • Scandent - a stem that climbs.Plant anatomy, From Wikipedia, the free encyclopedia 14
  • 15. • Stolon - a horizontally growing stem similar to a rhizome, but growing above or along the ground. • Tendril - a thigmotropic organ which attached a climbing plant to a support o Leaf - the photosynthetic organ of a plant o Stem - vascular tissue that provides support for the plant • Terminal - • Terminal scale bud scar - • Thorn - • Tiller - • Tuber - • Twigs - • Opposite - buds are arranged in pairs on opposite sides of the branch • Pith - • Pore - • Rhizome - • Sapwood - • Stoma - • Vascular bundles - • Verticil - a whorl of leaves or flowers. o Verticillate - arranged in whorls. • Whorled - said of a collection of three or more leaves or flowers that arise from the same point.Buds • Accessory - • Adventitious - • Axillary - • Dormant - • Flower bud - • Lateral - • Leaf bud - • Mixed - buds that have both embryonic flowers and leaves. • Naked - • Pseudoterminal - • Reproductive - buds with embryonic flowers. • Scaly - • Terminal - bud at the tip or end of the stem. • Vegetative - buds containing embryonic leaves.LeavesLeaf Parts: - A complete leaf is composed of a blade, petiole and stipules and in manyplants one or more might be lacking or highly modified. • Blade - • Petiole - • Stipules - a pair of outgrowths from the base of the leaf petiole. • Stipuloid - resembling stipules.Duration of leaves: • Deciduous -Plant anatomy, From Wikipedia, the free encyclopedia 15
  • 16. • Evergreen - • Fugacious - • Marcescent - • Persistent -Venation: • Acrodramous - when the veins run parallel to the leaf edge and fuse at the leaf tip. • Actinodromous - when the main veins of a leaf radiate from the tip of the petiole. • Vein - the externally visible vascular bundles, found on leafs, petals and other parts. • Veinlet - a small vein.Leaf Arrangement or Phyllotaxy: • Whorl - three or more leaves or branches or pedicels arising from the same node.Leaf Type: • Abruptly pinnate - a compound leaf without a terminal leaflet.Leaf Blade Shape: Main article: Leaf shape • Acicular (acicularis): Slender and pointed, needle-like • Acuminate (acuminata): Tapering to a long point • Aristate (aristata): Ending in a stiff, bristle-like point • Bipinnate (bipinnata): Each leaflet also pinnate • Cordate (cordata): Heart-shaped, stem attaches to cleft • Cuneate (cuneata): Triangular, stem attaches to point • Deltoid (deltoidea): Triangular, stem attaches to side • Digitate (digitata): Divided into finger-like lobes • Elliptic (elliptica): Oval, with a short or no point • Falcate (falcata): sickle-shaped • Flabellate (flabellata): Semi-circular, or fan-like • Hastate (hastata): shaped like a spear point, with flaring pointed lobes at the base • Lance-shaped, lanceolate (lanceolata): Long, wider in the middle • Linear (linearis): Long and very narrow • Lobed (lobata): With several points • Obcordate (obcordata): Heart-shaped, stem attaches to tapering point • Oblanceolate (oblanceolata): Top wider than bottom • Oblong (oblongus): Having an elongated form with slightly parallel sides • Obovate (obovata): Teardrop-shaped, stem attaches to tapering point • Obtuse (obtusus): With a blunt tip • Orbicular (orbicularis): Circular • Ovate (ovata): Oval, egg-shaped, with a tapering point • Palmate (palmata): Divided into many lobes • Pedate (pedata): Palmate, with cleft lobes • Peltate (peltata): Rounded, stem underneath • Perfoliate (perfoliata): Stem through the leaves • Pinnate (pinnata): Two rows of leaflets o odd-pinnate : pinnate with a terminal leaflet o paripinnate, even-pinnate : pinnate lacking a terminal leaflet • Pinnatisect (pinnatifida): Cut, but not to the midrib (it would be pinnate then)Plant anatomy, From Wikipedia, the free encyclopedia 16
  • 17. • Reniform (reniformis): Kidney-shaped • Rhomboid (rhomboidalis): Diamond-shaped • Round (rotundifolia): Circular • Sagittate (sagittata): Arrowhead-shaped • Spatulate, spathulate (spathulata): Spoon-shaped • Spear-shaped (hastata): Pointed, with barbs • Subulate (subulata): Awl-shaped with a tapering point • Sword-shaped (ensiformis): Long, thin, pointed • Trifoliate, ternate (trifoliata): Divided into three leaflets • Tripinnate (tripinnata): Pinnately compound in which each leaflet is itself bipinnate • Truncate (truncata): With a squared off end • Unifoliate (unifoliata): with a single leafLeaf Base Shape: • Semiamplexicaul - the leaf base wraps around the stem, but not completely.Leaf Blade Apex: • Acuminate - narrowing to a point, used for other structures too. • Acute - with a sharp rather abrupt ending point. o Acutifolius - with acute leaves. • Attenuate - tapering gradually to a narrow end.Leaf Blade Margins: • Crenulate - with shallow, small rounded teeth.Leaf Modifications:Epidermis and periderm texture • Acanceous - being prickly. • Acantha - a prickle or spine. • Acanthocarpus - fruits are spiny. • Acanthocladous - the branches are spiny. • Aculeate - having a covering of prickles or needle-like growth. o Aculeolate - having spine-like processes. • Aden - a gland. o Adenoid - gland like. o Adenophore - a stalk that supports a gland. o Adenophyllous - leaves with glands. • Arachnoid - having a cobwebby appearance with entangled hairs. • Bloom - the waxy coating that covers some plants. • Canescent - with gray pubescence. • Ciliate - with a fringe of marginal hairs. • Coriaceouse - with a tough or leathery texture. • Fimbriate - finely cut into fringes, the edge of a frilly petal or leaf. • Floccose - • Glabrate - • Glabrous - smooth without any pubescences at all. • Glandular - • Glandular-punctate - covered across the surface with glands. • Hirsute - with long shaggy hairs, often stiff or bristly to the touch.Plant anatomy, From Wikipedia, the free encyclopedia 17
  • 18. • Lanate - with woolly hairs. Thick wool like hairs. • Verrucose - with a wart surface, with low rounded bumps. • Villose - covered with fine long hairs that are not matted. o Villosity - villous indument.Floral morphology • Accrescent - Growing larger after anthesis, normally used for the calyx. • Anthesis - the period when the flower is fully open and functional.Basic flower parts • Acephalous - without a head, used for flower styles without a well-developed stigma. • Androecium - the stamens collectively. o Basifixed - attached by the base. o Connective - the part of the stamen joining the anther cells. o Diadelphous - o Didynamous - o Epipetalous - born on the corolla, often used in reference to stamens attached to the corolla. o Exserted - sticking out past the corolla, the stamens protrude past the margin of the corolla lip. o Extrose - opening towards the outside of the flower. o Gynandrium - combined male & female structure o Gynostregium - o Included - o Introrse - opening on the inside of the corolla, the stamens are contained within the margins of the petals. o Monodelphous - stamen filaments united into a tube. o Poricidal - anthers opening by terminal pores. o Staminode - a sterile stamen. Staminodial - flowers with sterile stamen. o Synanthamous - o Syngenesious - the anthers are united into a tube, the filaments are free. o Tetradynamous - o Translator - a structure uniting the pollinia in Asclepiadaceae and Orchidaceae. o Trinucleate - pollen containing three nuclei when shed. o Valvular - anthers opening by valves or small flaps, e.g. Berberis. o Versatile - anthers pivoting freely on the filament. • Anther - The distal end of the stamen where pollen is produced, normally composed of two parts called anther-sacs and pollen-sacs (thecae). • Bract - The leaf-like or scale-like leafy appendages that are located just below a flower, a flower stalk, or an inflorescence; they usually are reduced in size and sometimes showy or brightly colored.Plant anatomy, From Wikipedia, the free encyclopedia 18
  • 19. • Calyx -The whorl of sepals at the base of a flower. • Carpel -The ovule-producing reproductive organ of a flower, consisting of the stigma, style and ovary. • Corolla -The whorl of petals of a flower. • Disk - an enlargement or outgrowth from the receptacle of the flower, located at the center of the flower of various plants. The term is also use as the central area of the head in composites were the tubular flowers are attached. • Filament - The stalk of a stamen • Floral axis - • Floral envelope - • Flower - • Fruit - a structure contain all the seeds produced by a single flower. • Gynoecium - The whorl of carpels. May comprise one (syncarpous) or more (apocarpous) pistils. Each pistil consists of an ovary, style and stigma (female reproductive organs of the flower). o Apocarpus - The gynoecium comprises more than one pistil. o Cell - o Compound pistil - o Funicle - the stalk that connects the ovule to the placenta. o Funiculus - o Loculus - the cavities located with in a carpel, ovary or anther. o Locule - o multicarpellate - o Placentra - o Placentation - Axile - Basal - Free-central - Pariental - o Septum - o Simple pistil - o Syncarpous - The gynoecium comprises one pistil. o Unicarpellate - • Hypanthium - • Nectar - a fluid produce by nectaries high in sugar content, used to attract pollinators. • Nectary - a gland that secrets nectar, most often found in flowers but also produced on other parts of plants too. • Nectar disk - when the floral disk contains nectar secreting glands, often modified as its main function in some flowers. • Ovary - • Ovules - • Pedicel - the stem or stalk that holds a single flower in an inflorescence. • Peduncle - The part of a stem that bears the entire inflorescence, normally having no leaves or the leaves are reduce to bracts. When the flower is solitary, it is the stem or stalk holding the flower.Plant anatomy, From Wikipedia, the free encyclopedia 19
  • 20. o Peduncular - referring to or having a peduncle. o Pedunculate - having a peduncle. • Perianth - o Achlamydeous - without a perianth. • Petal - • Pistil - • Pollen - • Rachis - • Receptacle - the end of the pedicel that joins to the flower were the different parts of the flower are joined together, also called the torus. In Asteraceae the top of the pedicel upon which the flowers are joined. • Seed - • Sepal - • Stamen - • Staminode - • Stigma - • Style - • Tepal -Inflorescences • Capitulum - the flowers are arranged into a head composed of many separate unstalked flowers, the single flowers are called florets and are packed close together. The typical arrangement of flowers in the Asteraceae. • Compound Umbel - is an umbel where each stalk of the main umbel produces another smaller umbel of flowers. • Corymb - a grouping of flowers where all the flowers are at the same level, the flower stalks of different lengths forming a flat-topped flower cluster. • Cyme - is a cluster of flowers were the end of each growing point produces a flower. New growth comes from side shoots and the oldest and first flowers to bloom are at the top. • Single - one flower per stem or the flowers are greatly spread-apart as to appear they do not arise from the same branch. • Spike - when flowers arising from the main stem are without individual flower stalks. The flowers attach directly to the stem. • Solitary - same as single, with one flower per stem. • Raceme - is a flower spike with flowers that have stalks of equal length. The stem tip continues to grow and produce more flowers with the bottom flowers open first and blooming progresses up the stem. • Panicle - is a raceme with branches and each branch having a smaller raceme of flowers. The terminal bud of each branch continues to grow, producing more side shoots and flowers. • Pedicel - stem holding a one flower in an inflorescences. • Peduncle - stem holding an inflorescences, or a single flower. • Umbel - were the flower head has all the flower stalks rising from the same point of the same length, the flower head is rounded like an umbrella or almost circular.Plant anatomy, From Wikipedia, the free encyclopedia 20
  • 21. • Verticillaster - a whorled collection of flowers around the stem, the flowers produced in rings at intervals up the stem. As the stem tip continues to grow more whorls of flowers are produced. Typical in Lamiaceae. o Verticil - flowers arranged in whorls at the nodes.Insertion of floral parts • Epigynous - • Half-inferior - • Hypogynous - • Inferior - • Insertion - o Stamens - o Ovary - • Perigynous - • Superior -Specialized terms • Wing - term used for the lateral petals of the flowers on species in Fabaceae and Polygalaceae. • Valvate - meeting along the margins but not overlapping.Union of flower parts • Adelphous - the androecium with the stamen filaments partly or completely fused together.Flower sexuality and presence of floral parts • Achlamydeous - flower without a perianth. • Apetalous - a flower without petals. • Accrescent - said of the calyx when it is persistent and enlarges as the fruit grows and ripens, applied to other structure sometimes. • Androgymous - used for the inflorescence of Carex when a spike has both staminate and pistillate flowers - the pistillate flowers are normally at the base of the spike. • Bisexual - • Complete - • Imperfect - • Naked -Flower symmetry • Actinomorphic - having a radial symmetry, as in regular flowers. o Actinomorphy - when the flower parts are arranged with radial symmetry. • Dialypetalae - • Incomplete - • Perfect - • Radial - • Unisexual - • Zygomorphic - one axis of symmetry running down the middle of the flower so the right and left halves reflect each other.Plant anatomy, From Wikipedia, the free encyclopedia 21
  • 22. o Zygomorphy - the type of symmetry that most irregular flowers have with the upper half of the flower unlike the lower half. the left and right halves tend to be mirror images of each other.Pollination and fertilization • Allogamy – cross pollination, when one plant pollinates another plant • Anemophilous – wind pollinated. • Autogamy – self-pollination, when the flowers of the same plant pollinate flowers on the same plant or themselves. • Cantharophilous – beetle pollinated • Chiropterophilous - bat pollinated. • Cleistogamous – self-pollination of a flower that does not open. • Dichogamy – Flowers that cannot pollinate themselves because pollen is produced at a time when the stigmas are not receptive of pollen. • Entomophilous – insect pollinated. • Hydrophilous – Water pollinated, pollen is moved in water from one flower to the next. • Malacophilous – pollinated by snails and slugs. • Ornithophilous – pollinated by birds. • Pollination – the movement of pollen from the anther to the stigma. • Protandrous – when pollen is produced and shed before the carpels are mature. • Progynous – when the carpels mature before the stamens produce pollen.Embryo development • Antipodal cell - • Chalazal - • Coleoptile - • Coleorhiza - • Cotyledon - • Double ferilization - • Embryo – • Embryo sac - • Endosperm – • Filiform apparatus - • Germination – • Plumule - • Polar nuclei - • Radicle - • Scutellum - • Synergid - • Tegmen - • Testa - • Triploid - • Xenia - • Zygote –Plant anatomy, From Wikipedia, the free encyclopedia 22
  • 23. Fruits and seedsFruits are the matured ovary of seed bearing plants and they include the contents of theovary, which can be floral parts like the receptacle, involucre, calyx and others that arefused to it. Fruits are often used to identify plant taxa and help to place the species in thecorrect family or differentiate different groups with in the same family.Terms for fruits • Accessory structures - parts of fruits that do not form from the ovary. • Beak - normally the slender elongated end of a fruit, typically a persistent style- base. • Circumscissile - a type of fruit dehiscences were the top of the fruit falls away like a lid or covering. • Dehiscent - the way a fruit openings and releases its contents, normally in a regular and distinctive fashion. • Endocarp - includes the wall of the seed chamber, the inner part of the pericarp. • Exocarp - the pericarps outer part. • Fleshy - soft and juicy. • Indehiscent - fruits that do not have specialized structures for opening and releasing the seeds, they remain closed after the seeds ripen and are opened by animals, weathering, fire or other external means. • Mesocarp - the middle layer of the pericarp. • Pericarp - the body of the fruit from its outside surface to the chamber were the seeds are, including the outside skin of the fruit and the inside lining of the seed chamber. • Suture - the seam along which the fruit opens, normally in most fruits it is were the carpel or carpels are fused together. • Valve - one of the segments of the capsule.Fruit typesFruits are divided into different types depending on how they form, were or how theyopen and what parts they are composed of. • Achaenocarp - see achene. • Achene - dry indehiscent fruit, they have one seed and form from a single carpel, the seed is distinct from the fruit wall. • Drupe - outer fleshy part surrounds a shell with a seed inside. • Utricle - a small inflated fruit with one seed that has thin walls,Seedless reproductionPteridophyte sporangium terms • Acrostichoid sorus - having several fused sori. • Annulus -outer part of sporangium • Elater - • Indusium - • Marginal - • Peltate - • Reniform - • Sporophyll - • Sorus / Sori -Plant anatomy, From Wikipedia, the free encyclopedia 23
  • 24. • Strobilus - • Submarginal -Bryophyte gametangium terms • Acrandrous - used for moss species that have antheridia at the top of the stem. • Acrocarpous - In mosses, bearing the sporophyte at the axix of the main shoot • Acrogynous - In liverworts, the female sex organs terminate the main shoot • Anacrogynous - In liverworts, female sex organs are produced by a lateral cell, thus the growth of the main shoot is indeterminate • Androcyte - • Androecium - • Androgynous - Monoicous, and producing both types of sex organs together. • Antheridiophore - A specialised branch that bears the antheridia in the Marchantiales • Antherozoid - • Archegoniophore - A specialised branch that bears the archaegonia in the Marchantiales • Autoicous - Produces male and female sex organs on the same plant but on separate inflorescences • Bract - • Cladautoicous - Male and female inflorescences on separate branches of the same plant • Dioicous - Having two forms of gametophyte, one form bearing antheridia and one form bearing archegonia. • Gonioautoicous - Male is bud-like in the axil of a female branch • Inflorescence - • Involucre - A tube of thallus tissue that protects the archegonia • Monoicous - Having a single form of gametophyte bearing both antheridia and archegonia, either together or on separate branches. • Paraphyses - Sterile hairs surrounding the archegonia and antheridia • Perianth - A protective tube that surrounds the archegonia, characterises the Jungermannialean liverworts • Perichaetium - The cluster of leaves with the enclosed female sex organs • Perigonium - The cluster of leaves with the enclosed male sex organs • Pseudautoicous - Dwarf male plants growing on living leaves of female plants • Pseudomonoicous - • Pseudoperianth - An involucre that resembles a perianth, but is made of thallus tissue, and usually forms after the sporophyte develops • Rhizautoicous - Male inflorescence attached to the female stem by rhizoids • Synoicous - Male and female sex organs on the same gametophyte but are not clusteredBryophyte sporangium terms • Amphithecium - • Anisosporous - • Annulus - in mosses, cells with thick walls along the rim of the sporangium and were the peristome teeth are attached. • Apophysis -Plant anatomy, From Wikipedia, the free encyclopedia 24
  • 25. • Archesporium - • Arthrodontous - • Articulate - • Astomous - • Basal membrane - • Calyptra - • Capsule - • Cleistocarpous - • Columella - • Dehisce - • Diplolepidous - • Divisural line - • Elater - • Endostome - • Endothecium - • Epiphragm - • Exostome - • Exothecium - • Foot - • Gymnostomous - • Haplolepidous - • Haustorium - • Hypophysis - • Immersed - • Indehiscent - • Inoperculate - • Nematodontous - • Nurse cells - • Operculate - • Operculum - • Oral - • Peristome - • Pseudoelater - • Seta - • Sporangium - • Stegocarpous - • Stoma - • Suboral - • Tapetum - • Trabecula - • Valve -See also • Glossary of botanical termsReferences 1. ^ Comparative morphology 2. ^ "glossary". Fire Effects Information System.Plant anatomy, From Wikipedia, the free encyclopedia 25
  • 26. Sources • Jones, Samuel B., and Arlene E. Luchsinger. 1979. Plant systematics. McGraw- Hill series in organismic biology. New York: McGraw-Hill. • Usher, George, and George Usher. 1996. The Wordsworth dictionary of botany. Ware, Hertfordshire: Wordsworth Reference.Retrieved from "http://en.wikipedia.org/wiki/List_of_plant_morphology_terms"Plant evolutionary developmental biologyPlant anatomy, From Wikipedia, the free encyclopedia 26
  • 27. For a more ecological discussion on the evolution of plant morphology, refer toEvolutionary history of plantsEvolutionary developmental biology (evo-devo) refers to the study of developmentalprograms and patterns from an evolutionary perspective.[1] It seeks to understand thevarious influences shaping the form and nature of life on the planet. Evo-devo arose as aseparate branch of science only in the last decade.[2] Most of the synthesis in evo-devohas been in the field of animal evolution, one reason being the presence of elegant modelsystems like Drosophila, C.elegans, Zebrafish and Xenopus. However, in the past coupleof decades, a wealth of information on plant morphology, coupled with modernmolecular techniques has helped shed light on the conserved and unique developmentalpatterns in the plant kingdom also.Contents • 1 Historical perspective o 1.1 Before 1900 o 1.2 1900 to the present • 2 Organisms, databases and tools • 3 Evolution of plant morphology o 3.1 Overview of plant evolution o 3.2 Evolution of meristems 3.2.1 Diversity in meristem architectures 3.2.2 Role of the KNOX-family genes 3.2.3 Evolution of the meristem architecture o 3.3 Evolution of leaves 3.3.1 Origins of the leaf 3.3.2 Factors influencing leaf architectures 3.3.3 Genetic evidences for leaf evolution o 3.4 Evolution of flowers 3.4.1 Origins of the flower 3.4.2 Evolution of the MADS-box family 3.4.3 Factors influencing floral diversity 3.4.4 Flowering time 3.4.5 Theories of flower evolution o 3.5 Evolution of secondary metabolism • 4 Mechanisms and players in evolution • 5 See also • 6 Suggested readings • 7 ReferencesHistorical perspective Before 1900 Johann Wolfgang von Goethe The origin of the term "morphology" is generally attributed to Johann Wolfgang von Goethe. He was of the opinion that there is an underlying fundamental organisation (Bauplan) in the diversity of flowering plants. In his book titled The Metamorphosis of Plants, he proposed that thePlant anatomy, From Wikipedia, the free encyclopedia 27
  • 28. Bauplan enabled us to predict the forms of plants that had not yet been discovered.[3]Goethe also was the first to make the perceptive suggestion that flowers consist ofmodified leaves.In the middle centuries, several basic foundations of our current understanding of plantmorphology were laid down. Nehemiah Grew, Marcello Malpighi, Robert Hooke,Antonie van Leeuwenhoek, Wilhelm von Nageli were just some of the people whohelped build knowledge on plant morphology at various levels of organisation. It was thetaxonomical classification of Carolus Linnaeus in the eighteenth century though, thatgenerated a firm base for the knowledge to stand on and expand.[4] The introduction ofthe concept of Darwinism in contemporary scientific discourse also had had an effect onthe thinking on plant forms and their evolution.Wilhelm Hofmeister, one of the most brilliant botanists of his times, was the one todiverge away from the idealist way of pursuing botany. Over the course of his life, hebrought an interdisciplinary outlook into botanical thinking. He came up with biophysicalexplanations on phenomena like phototaxis and geotaxis, and also discovered thealternation of generations in the plant life cycle.[5]1900 to the presentArabidopsis thaliana. This flowering plant has been a model system for most of plantmolecular studiesThe past century witnessed a rapid progress in the study of plant anatomy. The focusshifted from the population level to more reductionist levels. While the first half of thecentury saw expansion in developmental knowledge at the tissue and the organ level, inthe latter half, especially since the 1990s, there has also been a strong impetus on gainingmolecular information.Edward Charles Jeffrey was one of the early evo devo researchers of the 20th century. Heperformed a comparative analyses of the vasculatures of living and fossil Gymnospermsand came to the conclusion that the storage parenchyma has been derived fromtracheids.[6] His research[7] focussed primarily on plant anatomy in the context ofphylogeny. This tradition of evolutionary analyses of plant architectures was furtheradvanced by Katherine Esau, best known for her book The Plant Anatomy. Her workfocussed on the origin and development of various tissues in different plants. Workingwith Cheadle, she also explained the evolutionary specialization of the phloem tissuewith respect to its function.Plant anatomy, From Wikipedia, the free encyclopedia 28
  • 29. In the meantime, by the beginning of the latter half of 1900s, Arabidopsis thaliana hadbegun to be used in some developmental studies. The first collection of Arabidopsisthaliana mutants were made around 1945.[8] However it formally became established as amodel organism only in 1998.[9]Wikispecies has information related to:ArabidopsisThe recent spurt in information on various plant-related processes has largely been aresult of the revolution in molecular biology. Powerful techniques like mutagenesis andcomplementation were made possible in Arabidopsis via generation of T-DNAcontaining mutant lines, recombinant plasmids, techniques like Transposon Tagging etc.Availability of complete physical and genetic maps,[10] RNAi vectors, rapidtransformation protocols are some of the technologies that have significantly altered thescope of the field.[11] Recently, there has also been a massive increase in the genome andEST sequences[12] of various non-model species, which, coupled with the Bioinformaticstools existing today, generate interesting opportunities in the field of plant evo devoresearch.Organisms, databases and toolsThe sampling of the Floral Genome ProjectThe most important model systems in plant development have been Arabidopsis andMaize. Maize has traditionally been the favorite of plant geneticists, while extensiveresources in almost every area of plant physiology and development are available forArabidopsis. Apart from these, Rice, Antirrhinum, Brassica, Tomato are also being usedin a variety of studies. The genomes of Arabidopsis and Rice have been completelyPlant anatomy, From Wikipedia, the free encyclopedia 29
  • 30. sequenced, while the others are in process.[13]. It must be emphasized here that theinformation from these "model" organisms form the basis of our developmentalknowledge. While Brassica has been used primarily because of its convenient location inthe phylogenetic tree in the mustard family, Antirrhinum is a convenient system forstudying leaf architecture. Rice has been traditionally used for studying responses tohormones like abscissic acid and gibberelin as well as responses to stress. However,recently, not just the domesticated rice strain, but also the wild strains have been studiedfor their underlying genetic architectures.[14]Some people have objected against extending the results of model organisms to the plantworld. One argument is that the effect of gene knockouts in lab conditions wouldnt trulyreflect even the same plants response in the natural world. Also, these supposedly crucialgenes might not be responsible for the evolutionary origin of that character. For thesereasons, a comparative study of plant traits has been proposed as the way to go now.[15]Since the past few years, researchers have indeed begun looking at non-model, "non-conventional" organisms using modern genetic tools. One example of this is the FloralGenome Project, which envisages to study the evolution of the current patterns in thegenetic architecture of the flower through comparative genetic analyses.[16] Like the FGP,there are several such ongoing projects that aim to find out conserved and diversepatterns in evolution of the plant shape. Expressed sequence tag (EST) sequences of quitea few non-model plants like Sugarcane, Apple, Lotus, Barley, Cycas, Coffee, to name afew, are available freely online. The Cycad Genomics Project,[17] for example, aims tounderstand the differences in structure and function of genes between gymnosperms andangiosperms through sampling in the order Cycadales. In the process, it intends to makeavailable information for the study of evolution of structures like seeds, cones andevolution of life cycle patterns. Presently the most important sequenced genomes from anevo-devo point of view include those of A.thaliana (a flowering plant), Poplar (a woodyplant), Physcomitrella patens (a bryophyte), Maize (extensive genetic information), andChlamydomonas reinhardtii (a green alga). The impact of such a vast amount ofinformation on understanding common underlying developmental mechanisms can easilybe realised.Apart from EST and genome sequences, several other tools like PCR, Yeast two hybridsystem, microarrays, RNA Interference, SAGE, QTL mapping etc. permit the rapid studyof plant developmental patterns. Recently, cross-species hybridization has begun to beemployed on microarray chips, to study the conservation and divergence in mRNAexpression patterns between closely related species.[18] Techniques for analyzing this kindof data have also progressed over the past decade. We now have better models formolecular evolution, more refined analysis algorithms and better computing power as aresult of advances in computer sciences.Evolution of plant morphologyOverview of plant evolution Main article: Evolutionary history of plantsEvidence suggests that an algal scum formed on the land 1,200 million years ago, but itwas not until the Ordovician period, around 500 million years ago, that land plantsappeared. These begun to diversify in the late Silurian period, around 420 million yearsago, and the fruits of their diversification are displayed in remarkable detail in an earlyDevonian fossil assemblage known as the Rhynie chert. This chert preserved early plantsPlant anatomy, From Wikipedia, the free encyclopedia 30
  • 31. in cellular detail, petrified in volcanic springs. By the middle of the Devonian periodmost of the features recognised in plants today are present, including roots, leaves andseeds. By the late Devonian, plants had reached a degree of sophistication that allowedthem to form forests of tall trees. Evolutionary innovation continued after the Devonianperiod. Most plant groups were relatively unscathed by the Permo-Triassic extinctionevent, although the structures of communities changed. This may have set the scene forthe evolution of flowering plants in the Triassic (~200 million years ago), whichexploded the Cretaceous and Tertiary. The latest major group of plants to evolve were thegrasses, which became important in the mid Tertiary, from around 40 million years ago.The grasses, as well as many other groups, evolved new mechanisms of metabolism tosurvive the low CO2 and warm, dry conditions of the tropics over the last 10million years.Evolution of meristemsThe meristematic cells give rise to various organs of the plant, and keep the plantgrowing. The Shoot Apical Meristem (SAM) gives rise to organs like the leaves andflowers. The cells of the apical meristems - SAM and RAM (Root Apical Meristem)-divide rapidly and are considered to be indeterminate, in that they do not possess anydefined end fate. In that sense, the meristematic cells are frequently compared to the stemcells in animals, that have an analogous behavior and function.Diversity in meristem architecturesIs the mechanism of being indeterminate conserved in the SAMs of the plant world? TheSAM contains a population of stem cells that also produce the lateral meristems while thestem elongates. It turns out that the mechanism of regulation of the stem cell numbermight indeed be evolutionarily conserved. The CLAVATA gene CLV2 responsible formaintaining the stem cell population in Arabidopsis is very closely related to the Maizegene FASCIATED EAR 2(FEA2) also involved in the same function.[19] Similarly, inRice, the FON1-FON2 system seems to bear a close relationship with the CLV signalingsystem in Arabidopsis.[20] These studies suggest that the regulation of stem cell number,identity and differentiation might be an evolutionarily conserved mechanism inmonocots, if not in angiosperms. Rice also contains another genetic system distinct fromFON1-FON2, that is involved in regulating stem cell number.[21] This example underlinesthe innovation that goes about in the living world all the time.Role of the KNOX-family genesNote the long spur of the above flower. Spurs attract pollinators and confer pollinatorspecificity. (Flower:Linaria dalmatica)Plant anatomy, From Wikipedia, the free encyclopedia 31
  • 32. Complex leaves of C.hirsuta are a result of KNOX gene expressionGenetics screens have identified genes belonging to the KNOX family in this function.These genes essentially maintain the stem cells in an undifferentiated state. The KNOXfamily has undergone quite a bit of evolutionary diversification, while keeping the overallmechanism more or less similar. Members of the KNOX family have been found inplants as diverse as Arabidopsis, rice, barley and tomato. KNOX-like genes are alsopresent in some algae, mosses, ferns and gymnosperms. Misexpression of these genesleads to formation of interesting morphological features. For example, among membersof Antirrhinae, only the species of genus Antirrhinum lack a structure called spur in thefloral region. A spur is considered an evolutionary innovation because it definespollinator specificity and attraction. Researchers carried out transposon mutagenesis inAntirrhinum, and saw that some insertions led to formation of spurs that were verysimilar to the other members of Antirrhinae[22], indicating that the loss of spur in wildAntirrhinum populations could probably be an evolutionary innovation.The KNOX family has also been implicated in leaf shape evolution (See below for amore detailed discussion). One study looked at the pattern of KNOX gene expression inA.thaliana, that has simple leaves and Cardamine hirsuta, a plant having complex leaves.In A.thaliana, the KNOX genes are completely turned off in leaves, but in C.hirsuta, theexpression continued, generating complex leaves.[23] Also, it has been proposed that themechanism of KNOX gene action is conserved across all vascular plants, because there isa tight correlation between KNOX expression and a complex leaf morphology.[24]Evolution of the meristem architectureThe meristem architectures do differ between angiosperms, gymnosperms andpteridophytes. The gymnosperm vegetative meristem lacks organization into distincttunica and corpus layers. They possess large cells called Central Mother Cells in themeristem. In angiosperms, the outermost layer of cells divides anticlinally to generate thenew cells, while in gymnosperms, the plane of division in the meristem differs fordifferent cells. However, the apical cells do contain organelles like large vacuoles andstarch grains, like the angiosperm meristematic cells.Plant anatomy, From Wikipedia, the free encyclopedia 32
  • 33. Pteridophytes, like fern, on the other hand, do not possess a multicellular apicalmeristem. They possess a tetrahedral apical cell, which goes on to form the plant body.Any somatic mutation in this cell can lead to hereditary transmission of that mutation.[25]The earliest meristem-like organization is seen in an algal organism from group Charalesthat has a single dividing cell at the tip, much like the pteridophytes, yet more simpler.One can thus see a clear pattern in evolution of the meristematic tissue, frompteridophytes to angiosperms. Pteridophytes, with a single meristematic cell;gymnosperms with a multicellular, but less defined organization and finally,angiosperms, with the highest degree of organization. The genetic innovations thatcontributed to this evolution are yet not clearly known.Evolution of leaves For a discussion on Evolution of Photosynthesis, see Photosynthesis.Origins of the leaf Further information: Evolutionary history of plants#leaves and MegaphyllLeaf lamina. The leaf architecture probably arose multiple times in the plant lineageLeaves are the primary photosynthetic organs of a plant. Based on their structure, they areclassified into two types - microphylls, that lack complex venation patterns andmegaphylls, that are large and with a complex venation. It has been proposed that thesestructures arose independently.[26] Megaphylls, according to the Telome hypothesis, haveevolved from plants that showed a three dimensional branching architecture, throughthree transformations - planation, which involved formation of a planar architecture,webbing, or formation of the outgrowths between the planar branches and fusion, wherethese webbed outgrowths fused to form a proper leaf lamina. Studies have revealed thatthese three steps happened multiple times in the evolution of todays leaves.[27]It has been proposed that the before the evolution of leaves, plants had the photosyntheticapparatus on the stems. Todays megaphyll leaves probably became commonplace some360mya, about 40my after the simple leafless plants had colonized the land in the earlyDevonian period. This spread has been linked to the fall in the atmospheric carbondioxide concentrations in the Late Paleozoic era associated with a rise in density ofstomata on leaf surface. This must have allowed for better transpiration rates and gasexchange. Large leaves with less stomata would have gotten heated up in the suns heat,but an increased stomatal density allowed for a better-cooled leaf, thus making its spreadfeasible[28][29].Plant anatomy, From Wikipedia, the free encyclopedia 33
  • 34. Factors influencing leaf architecturesSpiny leaves of Aciphylla squarrosa. It is thought that these leaves evolved as anadaptation against the now extinct MoasVarious physical and physiological forces like light intensity, humidity, temperature,wind speeds etc. are thought to have influenced evolution of leaf shape and size. It isobserved that high trees rarely have large leaves, owing to the obstruction they generatefor winds. This obstruction can eventually lead to the tearing of leaves, if they are large.Similarly, trees that grow in temperate or taiga regions have pointed leaves, presumablyto prevent nucleation of ice onto the leaf surface and reduce water loss due totranspiration. Herbivory, not only by large mammals, but also small insects has beenimplicated as a driving force in leaf evolution, an example being plants of the genusAciphylla, that are commonly found in New Zealand. The now extinct Moas fed uponthese plants, and its seen that the leaves have spines on their bodies, which probablyfunctioned to discourage the moas from feeding on them. Other members of Aciphyllathat did not co-exist with the moas, do not have these spines.[30]Genetic evidences for leaf evolution At the genetic level, developmental studies have shown that repression of the KNOX genes is required for initiation of the leaf primordium. This is brought about by ARP genes, which encode transcription factors. Genes of this type have been found in many plants studied till now, and the mechanism i.e. repression of KNOX genes in leaf primordia, seems to be quite conserved. Interestingly, expression of KNOX genes in leaves produces complex leaves. It is speculated that the ARP function arose quite early in vascular plant evolution, because members of the primitive group Lycophytes also have a functionally similar gene. Other players that have a conserved role in defining leaf primordia are the phytohormone auxin, gibberelin and cytokinin. The diversity of leavesPlant anatomy, From Wikipedia, the free encyclopedia 34
  • 35. One interesting feature of a plant is its phyllotaxy. The arrangement of leaves on the plantbody is such that the plant can maximally harvest light under the given constraints, andhence, one might expect the trait to be genetically robust. However, it may not be so. Inmaize, a mutation in only one gene called abphyl (ABNORMAL PHYLLOTAXY) wasenough to change the phyllotaxy of the leaves. It implies that sometimes, mutationaltweaking of a single locus on the genome is enough to generate diversity. The abphylgene was later on shown to encode a cytokinin response regulator protein.[31]Once the leaf primordial cells are established from the SAM cells, the new axes for leafgrowth are defined, one important (and more studied) among them being the abaxial-adaxial (lower-upper surface) axes. The genes involved in defining this, and the otheraxes seem to be more or less conserved among higher plants. Proteins of the HD-ZIPIIIfamily have been implicated in defining the adaxial identity. These proteins deviate somecells in the leaf primordium from the default abaxial state, and make them adaxial. It isbelieved that in early plants with leaves, the leaves just had one type of surface - theabaxial one. This is the underside of todays leaves. The definition of the adaxial identityoccurred some 200 million years after the abaxial identity was established[32]. One canthus imagine the early leaves as an intermediate stage in evolution of todays leaves,having just arisen from spiny stem-like outgrowths of their leafless ancestors, coveredwith stomata all over, and not optimized as much for light harvesting.How the infinite variety of plant leaves is generated is a subject of intense research. Somecommon themes have emerged. One of the most significant is the involvement of KNOXgenes in generating compound leaves, as in tomato (see above). But this again is notuniversal. For example, pea uses a different mechanism for doing the same thing[33][34].Mutations in genes affecting leaf curvature can also change leaf form, by changing theleaf from flat, to a crinky shape,[35] like the shape of cabbage leaves. There also existdifferent morphogen gradients in a developing leaf which define the leafs axis. Changesin these morphogen gradients may also affect the leaf form. Another very important classof regulators of leaf development are the microRNAs, whose role in this process has justbegun to be documented. The coming years should see a rapid development incomparative studies on leaf development, with many EST sequences involved in theprocess coming online.Evolution of flowersFor a more ecological discussion on the evolution of flowers, go to Flower orEvolutionary history of plantsThe pollen bearing organs of the early flower CrossothecaA flower is, arguably, one of the most beautiful products of evolution. Flower-likestructures first appear in the fossil records some ~130 mya, in the Cretaceous era[36].Plant anatomy, From Wikipedia, the free encyclopedia 35
  • 36. The flowering plants have long been assumed to have evolved from within thegymnosperms; according to the traditional morphological view, they are closely allied tothe gnetales. However, recent molecular evidence is at odds to this hypothesis,[37][38] andfurther suggests that gnetales are more closely related to some gymnosperm groups thanangiosperms,[39] and that gymnosperms form a distinct clade to the angiosperms,[39][37][38].Molecular clock analysis predicts the divergence of flowering plants (anthophytes) andgymnosperms to ~300 mya[40]Phylogeny of anthophytes and gymnosperms, from [41] Cycads Angiosperms Ginkgo Cycads Bennettitale Conifers s Anthophytes Bennettitales Ginkgo Gnetales Conifers Angiosperm Gnetale s s Traditional view Modern viewThe main function of a flower is reproduction, which, before the evolution of the flowerand angiosperms, was the job of microsporophylls and megasporophylls. A flower can beconsidered a powerful evolutionary innovation, because its presence allowed the plantworld to access new means and mechanisms for reproduction.Origins of the flowerAmborella trichopoda : Amborellaceae is considered the sister family of all floweringplants (magnified image)The family Amborellaceae is regarded as the sister family of all living flowering plants.That means members of this family were most likely the first flowering plants.It seems that on the level of the organ, the leaf may be the ancestor of the flower, or atleast some floral organs. When we mutate some crucial genes involved in flowerdevelopment, we end up with a cluster of leaf-like structures. Thus, sometime in history,the developmental program leading to formation of a leaf must have been altered togenerate a flower. There probably also exists an overall robust framework within whichPlant anatomy, From Wikipedia, the free encyclopedia 36
  • 37. the floral diversity has been generated. A example of that is a gene called LEAFY (LFY),which is involved in flower development in Arabidopsis. The homologs of this gene arefound in angiosperms as diverse as tomato, snapdragon, pea, maize and evengymnosperms. Interestingly, expression of Arabidopsis LFY in distant plants like poplarand citrus also results in flower-production in these plants. The LFY gene regulates theexpression of some gene belonging to the MADS-box family. These genes, in turn, act asdirect controllers of flower development.Evolution of the MADS-box familyThe members of the MADS-box family of transcription factors play a very important andevolutionarily conserved role in flower development. According to the ABC Model offlower development, three zones - A,B and C - are generated within the developingflower primordium, by the action of some transcription factors, that are members of theMADS-box family. Among these, the functions of the B and C domain genes have beenevolutionarily more conserved than the A domain gene. Many of these genes have arisenthrough gene duplications of ancestral members of this family. Quite a few of them showredundant functions.The evolution of the MADS-box family has been extensively studied. These genes arepresent even in pteridophytes, but the spread and diversity is many times higher inangiosperms[42]. There appears to be quite a bit of pattern into how this family hasevolved. Consider the evolution of the C-region gene AGAMOUS (AG). It is expressed intodays flowers in the stamens, and the carpel, which are reproductive organs. Itsancestor in gymnosperms also has the same expression pattern. Here, it is expressed inthe strobili, an organ that produces pollens or ovules[43]. Similarly, the B-genes (AP3 andPI) ancestors are expressed only in the male organs in gymnosperms. Their descendantsin the modern angiosperms also are expressed only in the stamens, the male reproductiveorgan. Thus, the same, then-existing components were used by the plants in a novelmanner to generate the first flower. This is a recurring pattern in evolution.Factors influencing floral diversityWikiversity has bloom time data for Linaria vulgaris on the Bloom ClockThe various shapes and colors of flowersHow is the enormous diversity in the shape, color and sizes of flowers established? Thereis enormous variation in the developmental program in different plants. For example,monocots possess structures like lodicules and palea, that were believed to be analogousto the dicot petals and carpels respectively.It turns out that this is true, and the variation isdue to slight changes in the MADS-box genes and their expression pattern in themonocots. Another example is that of a plant called Linaria vulgaris, which has twoPlant anatomy, From Wikipedia, the free encyclopedia 37
  • 38. kinds of flower symmetries-radial and bilateral. These symmetries are due to epigeneticchanges in just one gene called CYCLOIDEA.[44]Large number of petals in roses has probably been a result of human selectionArabidopsis has a gene called AGAMOUS that plays an important role in defining howmany petals and sepals and other organs are generated. Mutations in this gene give rise tothe floral meristem obtaining an indeterminate fate, and many floral organs keep ongetting produced. We have flowers like roses, carnations and morning glory, for example,that have very dense floral organs. These flowers have been selected by horticulturistssince long for increased number of petals. Researchers have found that the morphology ofthese flowers is because of strong mutations in the AGAMOUS homolog in these plants,which leads to them making a large number of petals and sepals.[45] Several studies ondiverse plants like petunia, tomato, Impatiens, maize etc have suggested that theenormous diversity of flowers is a result of small changes in genes controlling theirdevelopment[46].Some of these changes also cause changes in expression patterns of the developmentalgenes, resulting in different phenotypes. The Floral Genome Project looked at the ESTdata from various tissues of many flowering plants. The researchers confirmed that theABC Model of flower development is not conserved across all angiosperms. Sometimesexpression domains change, as in the case of many monocots, and also in some basalangiosperms like Amborella. Different models of flower development like the The fadingboundaries model, or the Overlapping-boundaries model which propose non-rigiddomains of expression, may explain these architectures.[47] There is a possibility that fromthe basal to the modern angiosperms, the domains of floral architecture have gotten moreand more fixed through evolution.Flowering timeAnother floral feature that has been a subject of natural selection is flowering time. Someplants flower early in their life cycle, others require a period of vernalization beforeflowering. This decision is based on factors like temperature, light intensity, presence ofpollinators and other environmental signals. We know that genes like CONSTANS (CO),FLC and FRIGIDA regulate integration of environmental signals into the pathway forflower development. Variations in these loci have been associated with flowering timevariations between plants. For example, Arabidopsis thaliana ecotypes that grow in thecold, temperate regions require prolonged vernalization before they flower, while thetropical varieties, and the most common lab strains, dont. We now know that thisvariation is due to mutations in the FLC and FRIGIDA genes, rendering them non-functional.[48]Quite a few players in this process are conserved across all the plants studied. Sometimesthough, despite genetic conservation, the mechanism of action turns out to be different.Plant anatomy, From Wikipedia, the free encyclopedia 38
  • 39. For example, rice is a short-day plant, while Arabidopsis is a long-day plant. Now, inboth plants, the proteins CO and FLOWERING LOCUS T (FT) are present. But inArabidopsis, CO enhances FT production, while in rice, the CO homolog represses FTproduction, resulting in completely opposite downstream effects[49].Theories of flower evolution Main article: Evolutionary history of plants#flowersThere are many theories that propose how flowers evolved. Some of them are describedbelow.The Anthophyte Theory was based upon the observation that a gymnospermic groupGnetales has a flower-like ovule. It has partially developed vessels as found in theangiosperms, and the megasporangium is covered by three envelopes, like the ovarystructure of angiosperm flowers. However, many other lines of evidence show thatGnetales is not related to angiosperms.[41] Further information: anthophytaThe Mostly Male Theory has a more genetic basis. Proponents of this theory point outthat the gymnosperms have two very similar copies of the gene LFY while angiospermsjust one. Molecular clock analysis has shown that the other LFY paralog was lost inangiosperms around the same time as flower fossils become abundant, suggesting thatthis event might have led to floral evolution.[50] According to this theory, loss of one ofthe LFY paralog led to flowers that were more male, with the ovules being expressedectopically. These ovules initially performed the function of attracting pollinators, butsometime later, may have been integrated into the core flower.One theory also suggests that humans have been one of the reasons for the diversity offlowers. This theory suggests that since the early settlers found flowers beautiful, theymay have started selecting for them artificially.[51] The flowers may have evolved toexploit the ecological niche being opened because of humans finding them attractive. Thevalidity of this theory, however, is debatable, not least because flowers starteddiversifying long before they came into contact with humans.Evolution of secondary metabolismStructure of Azadirachtin, a terpenoid produced by the Neem plant, which helps ward offmicrobes and insects. Many secondary metabolites have complex structuresAlthough we know a lot of secondary metabolites produced by plants, the extent of thesame is still unfathomable. Secondary metabolites are essentially low molecular weightPlant anatomy, From Wikipedia, the free encyclopedia 39
  • 40. compounds, sometimes having complex structures. They function in processes as diverseas immunity, anti-herbivory, pollinator attraction, communication between plants,maintaining symbiotic associations with soil flora, enhancing the rate of fertilization etc,and hence are significant from the evo-devo perspective. The structural and functionaldiversity of these secondary metabolites across the plant kingdom is so huge that it isestimated that hundreds of thousands of enzymes might be involved in this process in theentire of the plant kingdom, with about 15-25% of the coding genome coding for theseenzymes. Despite this, every species has its unique arsenal of secondary metabolites.[52]Many of these metabolites are of enormous medical significance to humans.What is the purpose of having so many secondary metabolites being produced, with asignificant chunk of the metabolome devoted to this activity? It is hypothesized that mostof these chemicals help in generating immunity, and in consequence, the diversity ofthese metabolites is a result of a constant war between plants and their parasites. There isevidence that this may be true in many cases. The big question here is the reproductivecost involved in maintaining such an impressive inventory. Various models have beensuggested that probe into this aspect of the question, but a consensus on the extent of thecost is lacking.[53] We still cannot predict whether a plant with more secondarymetabolites would be better-off than other plants in its vicinity.Secondary metabolite production seems to have arose quite early during evolution. Evenbacteria possess the ability to make these compounds. But they assume more significantroles in life from fungi onwards to plants. In plants they seem to have spread out usingdifferent mechanisms like gene duplications, evolution of novel genes etc. Furthermore,studies have shown that diversity in some of these compounds may be positively selectedfor.Although the role of novel gene evolution in the evolution of secondary metabolismcannot be denied, there are several examples where new metabolites have been formed bysmall changes in the reaction. For example, cyanogen glycosides have been proposed tohave evolved multiple times in different plant lineages. There are several such instancesof convergent evolution. For example, we now know that enzymes for synthesis oflimonene - a terpene - are more similar between angiosperms and gymnosperms than totheir own terpene synthesis enzymes. This suggests independent evolution of thelimonene biosynthetic pathway in these two lineages.[54]Mechanisms and players in evolutionThe stem-loop secondary structure of a pre-microRNA from Brassica oleraceaWhile environmental factors are significantly responsible for evolutionary change, theyact merely as agents for natural selection. Change is inherently brought about viaphenomena at the genetic level - mutations, chromosomal rearrangements and epigeneticchanges. While the general types of mutations hold true across the living world, in plants,some other mechanisms have been implicated as highly significant.Plant anatomy, From Wikipedia, the free encyclopedia 40
  • 41. Polyploidy is a very common feature in plants. It is believed that at least half (andprobably all) plants are or have been polyploids. Polyploidy leads to genome doubling,thus generating functional redundancy in most genes. The duplicated genes may attainnew function, either by changes in expression pattern or changes in activity. Polyploidyand gene duplication are believed to be among the most powerful forces in evolution ofplant form. It is not know though, why genome doubling is such a frequent process inplants. One probable reason is the production of large amounts of secondary metabolitesin plant cells. Some of them might interfere in the normal process of chromosomalsegregation, leading to polypoidy.Extreme left: teosinte, Extreme right: maize, middle: maize-teosinte hybridIn recent times, plants have been shown to possess significant microRNA families, whichare conserved across many plant lineages. In comparison to animals, while the number ofplant miRNA families are lesser than animals, the size of each family is much larger. ThemiRNA genes are also much more spread out in the genome than those in animals, wherewe find them clustered. It has been proposed that these miRNA families have expandedby duplications of chromosomal regions.[55] Many miRNA genes involved in regulationof plant development have been found to be quite conserved between plants studied.Domestication of plants like maize, rice, barley, wheat etc has also been a significantdriving force in their evolution. Some studies have tried to look at the origins of themaize plant and it turns out that maize is a domesticated derivative of a wild plant fromMexico called teosinte. Teosinte belongs to the genus Zea, just as maize, but bears verysmall inflorescence, 5-10 hard cobs and a highly branched and spread out stem. Cauliflower : Brassica oleracea var botrytis Interestingly, crosses between a particular teosinte variety and maize yields fertile offsprings that are intermediate in phenotype between maize and teosinte. QTL analysis has also revealed some loci that when mutated in maize yield a teosinte- like stem or teosinte-like cobs. Molecular clock analysis of these genes estimates their origins to some 9000 years ago, wellin accordance with other records of maize domestication. It is believed that a small groupof farmers must have selected some maize-like natural mutant of teosinte some 9000years ago in Mexico, and subjected it to continuous selection to yield the maize plant aswe know today.[56]Plant anatomy, From Wikipedia, the free encyclopedia 41
  • 42. Another interesting case is that of cauliflower. The edible cauliflower is a domesticatedversion of the wild plant Brassica oleracea, which does not possess the denseundifferentiated inflorescence called the curd, that cauliflower possesses. Wikispecies has information related to: Brassicaceae Cauliflower possesses a single mutation in a gene called CAL, controllingmeristem differentiation into inflorescence. This causes the cells at the floral meristem togain an undifferentiated identity, and instead of growing into a flower, they grow into alump of undifferentiated cells.[57] This mutation has been selected through domesticationat least since the Greek empire.See also • Evolutionary developmental biology • Plant morphology • Comparative phylogenetics • Plant evolution • Evolutionary history of plantsSuggested readings1) The Genetics of plant morphological evolution2) Plant evolution and development in a post-genomic context3) Evolution of leaf developmental mechanismsReferences 1. ^ Hall B (2000). "Evo-Devo or Devo-Evo - Does it matter?". Evolution and Development 2 (4): 177–178. doi:10.1046/j.1525-142x.2000.00003e.x. 2. ^ Goodman C, Coughlin B (2000). "The evolution of evo devo biology". Proc. Natl.Acad. Sci. 97 (9): 4424–4425. doi:10.1073/pnas.97.9.4424. 3. ^ Kaplan D (2001). "The Science of Plant Morphology: Definition, History and Role in Modern Biology". Am. J. Bot. 88 (10): 1711–1741. doi:10.2307/3558347. 4. ^ http://www.cas.muohio.edu/~meicenrd/ANATOMY/Ch0_History/history.html Plant Morphology: Timeline 5. ^ Kaplan D (2001). "The Science of Plant Morphology: Definition, History and Role in Modern Biology". Am. J. Bot. 88 (10): 1711–1741. doi:10.2307/3558347. 6. ^ Jeffrey CE (1925). "The Origin of Parenchyma in Geological Time". Proc. Natl. Acad. Sci. 11: 106–110. doi:10.1073/pnas.11.1.106. 7. ^ Collected Papers of Jeffrey EC 8. ^ TAIR: About [[Arabidopsis] 9. ^ Fink G (1998). "Anatomy of a Revolution". Genetics 149: 473–477. 10. ^ The Arabidopsis Information Resource 11. ^ Fink G (1998). "Anatomy of a Revolution". Genetics 149: 473–477. 12. ^ NCBI dbEST Statistics 13. ^ NCBI Plant Genomes Central 14. ^ Ge S. et al (1999). "Phylogeny of rice genomes with emphasis on origins of allotetraploid species". Proc. Natl. Acad. Sci. 96 (25): 14400–14405. doi:10.1073/pnas.96.25.14400. 15. ^ Cronk Q. (2001). "Plant evolution and development in a post-genomic context". Nat. Rev. Gen. 2: 607–619. doi:10.1038/35084556. 16. ^ The Floral Genome Project HomePlant anatomy, From Wikipedia, the free encyclopedia 42
  • 43. 17. ^ Cycad Genomics Project home 18. ^ Lai Z (2006). "Microarray analysis reveals differential gene expression in hybrid sunflower species". Molecular Ecology 15 (5): 1213–1227. doi:10.1111/j.1365- 294X.2006.02775.x. 19. ^ Taguchi-Shiobara et al (2001). "The fasciated ear2 gene encodes a leucine-rich repeat receptor-like protein that regulates shoot meristem proliferation in maize". Genes and Dev. 15 (20): 2755–2766. doi:10.1101/gad.208501. 20. ^ Suzaki T. (2006). "Conservation and Diversification of Meristem Maintenance Mechanism in Oryza sativa: Function of the FLORAL ORGAN NUMBER2 Gene". Plant and Cell Physiol. 47 (12): 1591–1602. doi:10.1093/pcp/pcl025. 21. ^ Suzaki T. (2006). "Conservation and Diversification of Meristem Maintenance Mechanism in Oryza sativa: Function of the FLORAL ORGAN NUMBER2 Gene". Plant and Cell Physiol. 47 (12): 1591–1602. doi:10.1093/pcp/pcl025. 22. ^ Golz J.F. (2002). "Spontaneous Mutations in KNOX Genes Give Rise to a Novel Floral Structure in Antirrhinum". Current Biol. 12 (7): 515–522. doi:10.1016/S0960- 9822(02)00721-2. 23. ^ Hay and Tsiantis (2006). "The genetic basis for differences in leaf form between Arabidopsis thaliana and its wild relative Cardamine hirsuta". Nat. Gen. 38: 942–947. doi:10.1038/ng1835. 24. ^ Bharathan G. et al (2002). "Homologies in Leaf Form Inferred from KNOXI Gene Expression During Development". Science 296 (5574): 1858–1860. doi:10.1126/science.1070343. 25. ^ Klekowski E. (2003). "Plant clonality, mutation, diplontic selection and mutational meltdown". Biol. J. Linn. Soc. 79 (1): 61–67. 26. ^ Crane and Kenrick (1997). "Diverted development of reproductive organs: A source of morphological innovation in land plants". Plant System. and Evol. 206 (1): 161–174. doi:10.1007/BF00987946. 27. ^ Piazza P, et al (2005). "Evolution of leaf developmental mechanisms". New Phytol. 167: 693–710. 28. ^ Beerling D. et al (2001). "Evolution of leaf-form in land plants linked to atmospheric CO2 decline in the Late Palaeozoic era". Nature 410: 352–354. doi:10.1038/35066546. 29. ^ A perspective on the CO2 theory of early leaf evolution 30. ^ Brown V, et al (1991). "Herbivory and the Evolution of Leaf Size and Shape". Phil. Transac.: Biol. Soc. 333 (1267): 265–272. doi:10.1098/rstb.1991.0076. 31. ^ Jackson D., Hake S. (1999). "Control of Phyllotaxy in Maize by the ABPHYL1 Gene". Development 126: 315–323. 32. ^ Cronk Q. (2001). "Plant evolution and development in a post-genomic context". Nat. Rev. Gen. 2: 607–619. 33. ^ Tattersall et al (2005). "The Mutant crispa Reveals Multiple Roles for PHANTASTICA in Pea Compound Leaf Development". Plant Cell 17 (4): 1046–1060. 34. ^ Bharathan and Sinha (Dec 2001). "The Regulation of Compound Leaf Development". Plant Physiol. 127 (4): 1533–1538. 35. ^ Nath U et al (2003). "Genetic Control of Surface Curvature". Science 299 (5611): 1404–1407. doi:10.1126/science.1079354. 36. ^ Lawton-Rauh A. et al (2000). "Molecular evolution of flower development". Trends in Ecol. and Evol. 15 (4): 144–149. 37. ^ a b Chaw, S.M.; Parkinson, C.L.; Cheng, Y.; Vincent, T.M.; Palmer, J.D. (2000). "Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers". Proceedings of the National Academy of Sciences 97 (8): 4086. doi:10.1073/pnas.97.8.4086.Plant anatomy, From Wikipedia, the free encyclopedia 43
  • 44. 38. ^ a b Soltis, D.E.; Soltis, P.S.; Zanis, M.J. (2002). "Phylogeny of seed plants based on evidence from eight genes" (abstract). American Journal of Botany 89 (10): 1670. doi:10.3732/ajb.89.10.1670. Retrieved on 2008-04-08. 39. ^ a b Bowe, L.M.; Coat, G.; Depamphilis, C.W. (2000). "Phylogeny of seed plants based on all three genomic compartments: Extant gymnosperms are monophyletic and Gnetales closest relatives are conifers". Proceedings of the National Academy of Sciences 97 (8): 4092. doi:10.1073/pnas.97.8.4092. 40. ^ Nam, J. (2003). "Antiquity and Evolution of the MADS-Box Gene Family Controlling Flower Development in Plants". Mol. Biol. Evol. 20 (9): 1435–1447. doi:10.1093/molbev/msg152. 41. ^ a b Crepet, W. L. (2000). "Progress in understanding angiosperm history, success, and relationships: Darwins abominably "perplexing phenomenon"". Proceedings of the National Academy of Sciences 97: 12939. doi:10.1073/pnas.97.24.12939. PMID 11087846. 42. ^ Medarg NG and Yanofsky M (March 2001). "Function and evolution of the plant MADS-box gene family". Nat Rev Gen 2: 186–195. 43. ^ Jager et al (2003). "MADS-Box Genes in Ginkgo biloba and the Evolution of the AGAMOUS Family". Mol. Biol. and Evol. 20 (5): 842–854. doi:10.1093/molbev/msg089. 44. ^ Lawton-Rauh A. et al (2000). "Molecular evolution of flower development". Trends in Ecol. and Evol. 15 (4): 144–149. 45. ^ Kitahara K and Matsumoto S. (2000). "Rose MADS-box genes ‘MASAKO C1 and D1’ homologous to class C floral identity genes". Plant Science 151: 121. 46. ^ Kater M et al (1998). "Multiple AGAMOUS Homologs from Cucumber and Petunia Differ in Their Ability to Induce Reproductive Organ Fate". Plant Cell 10: 171–182. doi:10.1105/tpc.10.2.171. 47. ^ Soltis D et al (2007). "The floral genome: an evolutionary history of gene duplication and shifting patterns of gene expression". Trends in Plant Sci. 12 (8): 358–367. 48. ^ Putterhill et al (2004). "Its time to flower: the genetic control of flowering time". BioEssays 26 (4): 353–363. 49. ^ Blazquez et al (2001). "Flowering on time: genes that regulate the floral transition ". EMBO Reports 2 (12): 1078–1082. 50. ^ Lawton-Rauh A. et al (2000). "The Mostly Male Theory of Flower Evolutionary Origins: from Genes to Fossils". Sys.Botany 25 (2): 155–170. doi:10.2307/2666635. 51. ^ Haviland-Jones J. et al (2005). "An Environmental Approach to Positive Emotion: Flowers". Evol. Psychology 3: 104–132. 52. ^ Pichersky E. and Gang D. (2000). "Genetics and biochemistry of secondary metabolites in plants: an evolutionary perspective". Trends in Plant Sci 5 (10): 439–445. 53. ^ Nina Theis and Manuel Lerdau (2003). "The evolution of function in plant secondary metabolites". Int. J.Plant. Sci 164 (S3): S93–S102. 54. ^ Bohlmann J. et al (1998). "Plant terpenoid synthases: molecular and phylogenetic analysis". Proc.Natl.Acad.Sci. 95: 4126–4133. 55. ^ Li A and Mao L. (2007). "Evolution of plant microRNA gene families". Cell Research 17: 212–218. 56. ^ Doebley J.F. (2004). "The genetics of maize evolution". Ann. Rev. Gen 38: 37–59. 57. ^ Purugannan et al (2000). "Variation and Selection at the CAULIFLOWER Floral Homeotic Gene Accompanying the Evolution of Domesticated Brassica olerace". Genetics 155: 855–862.Plant anatomy, From Wikipedia, the free encyclopedia 44
  • 45. Sepal (Calyx) This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (March 2008) Tetramerous flower of Ludwigia octovalvis showing petals and sepals. A sepal (from Latin separatus "separate" + petalum "petal") is a part of the flower of angiosperms or flower plants. Sepals in a "typical" flower are green and lie under the more conspicuous petals. As a collective unit the sepals are called the calyx of a flower. The calyx is part of the perianth of the flower. The perianth is composed of the sepals (collectively called the calyx) and the corolla (which is the outer part of the flower with the inner part of the perianth composed of the petals). The petals andsepals are usually differentiated into colorful petals and green sepals. But many flowershave colorful sepals and lack petals or the sepals and petals look similar and are oftencalled tepals. The term tepal is usually applied when the petals and sepals are notdifferentiated and look similar or the petals are absent and the sepals are colorful. Whenthe flower is in bud, the sepals enclose and protect the more delicate floral parts within.Morphologically they are modified leaves.The number of sepals in a flower (called merosity) is indicative of the plantsclassification: eudicots having typically four or five sepals and monocots andpalaeodicots having three, or some multiple of three, sepals.There exists considerable variation in form of the sepals among the flowering plants.Often the sepals are much reduced, appearing somewhat awn-like, or as scales, teeth, orridges. Examples of flowers with much reduced perianths are found among the grasses.In some flowers, the sepals are fused towards the base, forming a calyx tube. This floraltube can include the petals and the attachment point of the stamens.See alsoPlant morphology (already placed) This botany article is a stub. You can help Wikipedia by expanding it.Retrieved from "http://en.wikipedia.org/wiki/Sepal"Plant anatomy, From Wikipedia, the free encyclopedia 45
  • 46. Petal (Redirected from Corolla (flower))Look up petal in Wiktionary, the free dictionary."Corolla (flower)" redirects here. For other uses, see Corolla.For the petals of chakras, see Petal (chakra).Tetrameric flower of the Primrose Willowherb (Ludwigia octovalvis) showing petals andsepalsThis tulip has dozens of petals.A petal (from Ancient Greek petalon "leaf", "thin plate"), regarded as a highly modifiedleaf, is one member or part of the corolla of a flower. The corolla is the name for all ofthe petals of a flower; the inner perianth whorl, term used when this is not the same inappearance (color, shape) as the outermost whorl (the calyx) and is used to attractpollinators based on its bright color. It is the inner part of the perianth that comprises thesterile parts of a flower and consists of inner and outer tepals. These tepals are usuallydifferentiated into petals and sepals. The term "tepal" is usually applied when the petalsand sepals are similar in shape and color. In a "typical" flower the petals are showy andcolored and surround the reproductive parts. The number of petals in a flower (seemerosity) is indicative of the plants classification: eudicots (the largest group of dicots)having typically four or five petals and monocots and magnoliids having three, or somemultiple of three, petals.[1]Plant anatomy, From Wikipedia, the free encyclopedia 46
  • 47. There exists considerable variation in form of petals among the flowering plants. Thepetals can be united towards the base, forming a floral tube. In some flowers, the entireperianth forms a cup (called a calyx tube) surrounding the gynoecium, with the sepals,petals, and stamens attached to the rim of the cup.The flowers of some species lack or have very much reduced petals. These are oftenreferred to as apetalous. Examples of flowers with much reduced perianths are foundamong the grasses.The petals are usually the most conspicuous parts of a flower, and the petal whorl orcorolla may be either radially or bilaterally symmetrical. If all of the petals are essentiallyidentical in size and shape, the flower is said to be regular or actinomorphic (meaningray-formed). Many flowers are symmetrical in only one plane (i.e., symmetry isbilateral) and are termed irregular or zygomorphic (meaning yoke- or pair-formed). Inirregular flowers, other floral parts may be modified from the regular form, but thepetals show the greatest deviation from radial symmetry. Examples of zygomorphicflowers may be seen in orchids and members of the pea family. The petal is the colorful,often showy part of a plant.Other structures which may look like petalsSome plants have petaloid stamens, in plants like Canna that have true petals andstaminodes, the stamen (staminodes) are modified to look like large showy petals.A number of plants have bracts that resemble petals for example in Bougainvillea andCornus florida (flowering dogwood). Petal-like bracts are common features in some plantfamilies like Euphorbiaceae.In many plants of the aster family such as the sunflower, Helianthus annuus, thecircumference of the flower head is composed of ray florets. Each ray floret isanatomically an individual flower with a single large petal.CorollaCorolla is the collective term for petals of a flower taken as a group within the calyx.Normally the corolla is the most conspicuous part of a flower and of a bright colour otherthan green. The concept of corolla description is widely used in botany as a primarydeterminant of vascular plant identification. Alternatively the corolla may be consideredas the inner whorl of the perianth structure. The role of the corolla in plant evolution hasbeen studied extensively since Darwin postulated a theory of the origin of elongatedcorollae.[2]References 1. ^ Pamela S. Soltis and Douglas E. Soltis (2004). "The origin and diversification of angiosperms". American Journal of Botany 91: 1614–1626. doi:10.3732/ajb.91.10.1614. 2. ^ Analysis of theory of evolution of corolla elongation involving pollinating speciesRetrieved from "http://en.wikipedia.org/wiki/Petal#Corolla"Categories: Plant morphology | Reproductive system | PollinationAmerican Journal of Botany. 2004;91:1614-1626.)© 2004 Botanical Society of America, Inc.Invited Special PapersPlant anatomy, From Wikipedia, the free encyclopedia 47
  • 48. The origin and diversification of angiosperms1Pamela S. Soltis2,4 and Douglas E. Soltis32 Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611 USA; 3Departmentof Botany, University of Florida, Gainesville, Florida 32611 USAReceived for publication February 6, 2004. Accepted for publication July 1, 2004.ABSTRACT The angiosperms, one of five groups of extant seed plants, are the largest group of landplants. Despite their relatively recent origin, this clade is extremely diversemorphologically and ecologically. However, angiosperms are clearly united by severalsynapomorphies. During the past 10 years, higher-level relationships of the angiospermshave been resolved. For example, most analyses are consistent in identifying Amborella,Nymphaeaceae, and Austrobaileyales as the basalmost branches of the angiosperm tree.Other basal lineages include Chloranthaceae, magnoliids, and monocots. Approximatelythree quarters of all angiosperm species belong to the eudicot clade, which is stronglysupported by molecular data but united morphologically by a single synapomorphy—triaperturate pollen. Major clades of eudicots include Ranunculales, which are sister to allother eudicots, and a clade of core eudicots, the largest members of which areSaxifragales, Caryophyllales, rosids, and asterids. Despite rapid progress in resolvingangiosperm relationships, several significant problems remain: (1) relationships amongthe monocots, Chloranthaceae, magnoliids, and eudicots, (2) branching order amongbasal eudicots, (3) relationships among the major clades of core eudicots, (4)relationships within rosids, (5) relationships of the many lineages of parasitic plants, and(6) integration of fossils with extant taxa into a comprehensive tree of angiospermphylogeny.Key Words: Amborella • angiosperms • phylogeny INTRODUCTIONThe angiosperms, or flowering plants, one of the major clades of extant seed plants (seeBurleigh and Mathews, 2004 , in this issue), are the largest group of embryophytes, withat least 260 000 living species classified in 453 families (APG II, 2003 ). Angiospermsare amazingly diverse. They occupy every habitat on Earth except the highestmountaintops, the regions immediately surrounding the poles, and the deepest oceans,and they occur as epiphytes, floating and rooted aquatics in both freshwater and marinehabitats, and terrestrial plants that vary tremendously in size, longevity, and overall form.Furthermore, the diversity in chemistry, reproductive morphology, and genome size andorganization is unparalleled in the Plant Kingdom.Despite their diversity, angiosperms are clearly united by a suite of synapomorphies (i.e.,shared, derived features), including double fertilization and endosperm formation, thecarpel, stamens with two pairs of pollen sacs, features of gametophyte structure anddevelopment, and phloem tissue composed of sieve tubes and companion cells (see Doyleand Donoghue, 1986 ; and P. Soltis et al., 2004 , for further discussion). This evidencestrongly negates hypotheses of polyphyletic origins of extant angiosperms.The fossil record of the angiosperms extends back at least to the early Cretaceous,conservatively 130 million years ago (mya) (see Crane et al., 2004 ). Floral size,structure, and organization among early angiosperms varied tremendously, ranging fromPlant anatomy, From Wikipedia, the free encyclopedia 48
  • 49. small (i.e., <1 cm in diameter) flowers of fossil Chloranthaceae and many other lineages(reviewed in Friis et al., 2000 ), both extant and extinct, to the large, Magnolia-likeflowers of Archaeanthus (Dilcher and Crane, 1984 ). This floral diversity in the fossilrecord is consistent with an early radiation of angiosperms and associated diversificationin floral form (e.g., Friis et al., 2000 ).Large-scale collaborations among angiosperm systematists have greatly improved ourunderstanding of angiosperm phylogeny. Strong support for many clades that correspondto traditionally recognized families provided early confidence that the molecular-basedtrees were producing reasonable reconstructions of phylogeny. However, some traditionalfamilies and many orders and higher groups have been shown to be nonmonophyletic,while many groups of previously uncertain placement have been placed with greatconfidence. The Angiosperm Phylogeny Group, an international consortium ofsystematists, recognized the need for a new classification that reflects current views ofangiosperm phylogeny (APG, 1998 ; APG II, 2003 ). An abridged version of theclassification is given in Appendix 1 (see Supplemental Data accompanying onlineversion of this paper) and at the Deep Time website (http://flmnh.ufl.edu/deeptime).In this paper, we provide a brief overview of angiosperm phylogeny as currentlyunderstood (Fig. 1) and examine patterns of angiosperm diversification. The monocot andeudicot clades will be considered in greater detail in the accompanying papers by Chase(2004) and Judd and Olmstead (2004) , respectively. Fig. 1. Overview of angiosperm phylogenetic relationships, based on Qiu et al. (1999) , P. Soltis et al. (1999) , D. Soltis et al. (2000 , 2003 ), Zanis et al. (2002) , Hilu et al. (2003) , Kim et al. (2004b) View larger version (29K): [in this window] [in a new window] ANGIOSPERM PHYLOGENYThe root of the treeA mere decade ago, the possibility of identifying the basal nodes of the angiosperm cladeseemed remote. However, most analyses of the past five years concur in placing themonotypic Amborella as the sister to all other extant angiosperms. Amborella trichopoda,Plant anatomy, From Wikipedia, the free encyclopedia 49
  • 50. endemic to cloud forests of New Caledonia, was described in the mid-nineteenth century(Baillon, 1869 ) and has since been classified with various groups of basal angiosperms,most often with Laurales (e.g., Cronquist, 1981 ). However, Amborella clearly differsfrom most Laurales in having spirally arranged floral organs (except perhaps the carpels;Buzgo et al., in press), rather than the whorled phyllotaxis typical of most Laurales (seestudies of floral morphology and development by Endress and Igersheim, 2000b ;Posluszny and Tomlinson, 2003 ; Buzgo et al., in press), and lacks those featuresconsidered to be synapomorphies for Laurales (Doyle and Endress, 2000 ; see Lauraleslater). Amborella has carpels that are closed only by secretion, rather than by fused tissueas in most angiosperms (Endress and Igersheim, 2000a )—a feature that may represent aplesiomorphy (i.e., ancestral feature) for the angiosperms. Vessels (Judd et al., 2002 ;but see Feild et al., 2000 ; Doyle and Endress, 2000 ) and pollen grains with a reticulatetectum (Doyle and Endress, 2001) appear to be synapomorphies for all extantangiosperms except Amborella. Ethereal oil cells—common throughout basalangiosperms—and columellate pollen grains with a perforate tectum are synapomorphiesfor all extant angiosperms except Amborella and Nymphaeaceae (Doyle and Endress,2001).The evidence for AmborellaNearly all multigene analyses of basal angiosperms have identified Amborella as thesister to all other extant angiosperms (e.g., Mathews and Donoghue, 1999 , 2000 ;Parkinson et al., 1999 ; Qiu et al., 1999 ; P. Soltis et al., 1999 ; Graham and Olmstead,2000 ; Graham et al., 2000 ; D. Soltis et al., 2000 ; Magallón and Sanderson, 2001 ;Zanis et al., 2002 ; see also Nickerson and Drouin, 2004 ), with varying levels ofsupport. The genes that support this position come from all three plant genomes andrepresent relatively "slowly evolving" protein-coding and ribosomal RNA genes.Furthermore, analyses of the "rapidly evolving" plastid gene matK (Hilu et al., 2003 )and mostly noncoding trnL-trnF (Borsch et al., 2003 ) each showed these same results.In all of these studies, Nymphaeaceae and Austrobaileyales (both sensu the AngiospermPhylogeny Group, APG II, 2003 ) "followed" Amborella as successive sisters to theremaining extant angiosperms. Furthermore, the structural organization of the floralMADS-box genes Apetala3 and Pistillata also supported the position of Amborella andNymphaeaceae as sisters to all other extant angiosperms, and analyses of nucleotide andamino acid sequences of these genes also placed Amborella, either alone or withNymphaeaceae, in this position (Kim et al., in press ).Alternative viewsDespite general support for the placement of Amborella as sister to the rest of the extantangiosperms, a few studies have found alternative rootings, using either different genes ordifferent methods of analysis. For example, Amborella + Nymphaeaceae (e.g., Parkinsonet al., 1999 ; Barkman et al., 2000 ; Mathews and Donoghue, 2000 ; Qiu et al., 2000; P. Soltis et al., 2000 ; Kim et al., in press ) or Nymphaeaceae alone (e.g., Parkinson etal., 1999 ; Graham and Olmstead, 2000 , with partial sampling of Nymphaeaceae;Mathews and Donoghue, 2000 ) have occasionally been reported as sister to all otherangiosperms. However, statistical analyses of these alternative rootings using a data set ofup to 11 genes generally favor the tree with Amborella as sister to the rest, although theAmborella + Nymphaeaceae tree could not always be rejected (Zanis et al., 2002 ).Nearly all of these studies are consistent in noting that conflicting topologies are notPlant anatomy, From Wikipedia, the free encyclopedia 50
  • 51. strongly supported. Furthermore, the difference among these three topologies is relativelyminor and consists solely of the relative placement of Amborella and Nymphaeaceae.A more dramatic alternative, based on a selection of 61 genes from the totally sequencedplastid genomes of 13 plant species, placed the monocots (represented only by threegrasses—rice, maize, and wheat) as the sister to all other extant angiosperms (Goremykinet al., 2003 ). Whereas all molecular analyses of angiosperms with dense taxon samplingstrongly supported monophyly of the monocots and most placed this clade among thebasal nodes of the angiosperm tree, none has indicated that monocots are sister to all otherextant angiosperms. In the analysis by Goremykin et al. (2003) , Amborella was sister toCalycanthus of Laurales, a position consistent with the original description of Amborella,but clearly at odds with other aspects of morphology (see Laurales section). Goremykin etal. (2003) attributed their results to the increased character sampling (30 017 nucleotidesin their aligned matrix) in their study relative to other analyses that included fewer genesbut many more taxa. However, further analyses of a data set of three genes and nearlyequivalent taxon sampling indicated that the "monocots basal" topology is an artifact oflimited taxon sampling (Soltis and Soltis, 2004 ). When either Nymphaea orAustrobaileya, representing Nymphaeaceae and Austrobaileyales, respectively, wassubstituted for Amborella, each appeared as the sister to Calycanthus, in exactly the sameposition that Amborella had occupied, presumably because the data set, which was limitedto a subset of those plant species for which entire plastid genome sequences are available,contained no other close relatives. Furthermore, representing monocots by taxa other thangrasses, which reside at the end of a long branch (e.g., Gaut et al., 1992 , 1996 ; Chaseet al., 2000 ), broke up the long branch to the monocots and resulted in the "Amborellabasal" topology. Likewise, broader sampling of the monocots beyond grasses (the solemonocots included by Goremykin et al., 2003 ) also severed the long monocot branchand yielded the "Amborella basal" tree. Finally, when plastid sequences of the monocotAcorus were added to the data set of Goremykin et al., also disrupting the long branch tothe grasses, Amborella resumed its position as sister to the other angiosperms (S.Stefanovic et al., Indiana University, unpublished data). Although increasing the numberof characters will generally lead to greater accuracy (Hillis, 1996 ) and support (e.g.,Givnish and Sytsma, 1997 ; Soltis et al., 1998 ), the increase in characters cannot comeat the expense of adequate taxon sampling (e.g., Chase et al., 1993 ; Sytsma and Baum,1996 ; Zwickl and Hillis, 2002 ; Pollock et al., 2002 ; Soltis et al., in press-a ).Limited taxon sampling, such as that dictated by the small number of organisms withcomplete genome sequences, may lead to artifacts, as apparently occurred in the analysisby Goremykin et al. (2003) .The fossil recordThe fossil record does not clarify basal groups within the angiosperms. However, itclearly identifies a number of morphologically diverse lineages early in angiospermevolution (e.g., Crane et al., 1995 ; Friis et al., 2000 ). Although some of these earlyfossils seem to belong to extant families, many do not fit easily into extant groups. Forexample, two species of Archaefructus (Sun et al., 1998 , 2002 ) may be the sister to allother angiosperms (Sun et al., 2002 ), although a reanalysis of their data, with theinclusion of additional material, indicated alternative placements (Friis et al., 2003 ).Notably, with regard to the plastid topology of Goremykin et al. (2003) , the monocotsare not among the earliest angiosperm fossils, although both the fossil record (Gandolfo etal., 2002 ) and molecular clock estimates (K. Bremer, 2000 ; Wikström et al., 2001 ;Plant anatomy, From Wikipedia, the free encyclopedia 51
  • 52. Davies et al., 2004 ) have indicated that many lineages of monocots date back at least80–100 mya. However, Nymphaeaceae are among the earliest angiosperm fossils: a waterlily from approximately 125 mya (Friis et al., 2001 ) is consistent with the basal or near-basal position of the Nymphaeaceae branch in most molecular-based trees, and the floralfeatures of Microvictoria (90 mya; Gandolfo et al., 2004 ) provide evidence of beetleentrapment pollination in early angiosperms. Likewise, the abundance of fossils ofChloranthaceae and Ceratophyllaceae from the early Cretaceous (e.g., Couper, 1958 ;Walker and Walker, 1984 ; Dilcher, 1989 ; Friis et al., 2000 ; see Endress, 2001 , forreview) is also consistent with the placement of these clades among extant angiosperms inmolecular-based trees (Figs. 1, 2). Fig. 2. Summary of phylogenetic relationships among clades of basal angiosperms, based primarily on Zanis et al. (2002) View larger version (34K): [in this window] [in a new window]Basal lineagesThe positions of Amborellaceae and Nymphaeaceae as successive sisters to the rest of theangiosperms are followed in turn by Austrobaileyales. Although these first three nodesare well supported (e.g., Zanis et al., 2002 ; Hilu et al., 2003 ), resolution and supportfor relationships of the next few nodes are poor (Fig. 2). Ceratophyllaceae, monocots,Chloranthaceae, magnoliids, and eudicots are each well supported, and both the fossilrecord and molecular-based trees identify these lineages as ancient. However, theirinterrelationships remain unclear. It is clear, however, that angiosperms do not fall intotwo major groups that correspond to monocots (Liliopsida) and dicots (Magnoliopsida) oflongstanding classification systems (such as Cronquist, 1981 ; Takhtajan, 1997 , andtheir predecessors). Although monocots clearly form a strongly supported clade, dicots inthe traditional sense do not: most are found in the eudicot clade, but the remainingnonmonocot basal branches (i.e., Amborellaceae, Nymphaeaceae, Austrobaileyales,Ceratophyllaceae, Chloranthaceae, magnoliids) were also "traditional" dicots. Thenonmonophyly of the dicots has long been suspected, and the lack of monophylyprecludes their recognition in current classifications (e.g., APG II, 2003 ). The conceptof "dicot" should be abandoned in favor of eudicots, with recognition that considerablediversity exists outside the monocot and eudicot clades.NymphaeaceaeThe phylogenetic position of Nymphaeaceae as one of the two basalmost lineages ofPlant anatomy, From Wikipedia, the free encyclopedia 52
  • 53. extant angiosperms is strongly supported by nearly all molecular analyses. This clade ofeight genera has a worldwide distribution, consistent with both the ancient age of thislineage and aquatic habitats. Although all genera occupy aquatic habitats, these habitatsrange from temperate to tropical. Floral diversity among genera is extensive, ranging fromthe small, simple, trimerous, monocot-like flowers of Cabomba to the large, showy,elaborate flowers of Nymphaea and Victoria. Although the latter were considered"primitive" by most authors, Schneider (1979) suggested that the numerous floral organsof Nymphaea and Victoria resulted from secondary increase. Phylogenetic analyses (Leset al., 1999 ) and character reconstructions (Ronse DeCraene et al., 2003 ; Soltis et al.,in press-b ) supported Schneiders (1979) hypothesis. Floral diversification inNymphaeacae may be related to changes in pollination: proliferation of parts in responseto beetle pollination in Nymphaea and Victoria and a reduction in number of partsassociated with a shift to cleistogamy in Euryale (Gottsberger, 1977 , 1978 ; Williamsand Schneider, 1993 ; Lipok et al., 2000 ).AustrobaileyalesThis small clade comprises Austrobaileyaceae (Austrobaileya) and Trimeniaceae(Trimenia) from Australasia plus Schisandraceae sensu APG II (2003) , i.e.,Schisandraceae (Schisandra and Kadsura) and Illiciaceae (Illicium) of most other recentclassifications (Qiu et al., 1999 ; Renner, 1999 ; Savolainen et al., 2000a , b ; P.Soltis et al., 1999 ; D. Soltis et al., 2000 ). Although the traditional Illiciaceae andSchisandraceae have typically been united in Illiciales, a relationship between these taxaand Austrobaileya and Trimenia had not been suspected. No morphologicalsynapomorphies have been identified for this clade, despite the strong molecular supportfor its monophyly.CeratophyllaceaeCeratophyllaceae (Ceratophyllum) had the distinction of appearing as the sister to allother angiosperms in the first large molecular phylogenetic analysis based on rbcL (Chaseet al., 1993 ). The aquatic habit and simple flowers seemed at odds with mosthypotheses about the earliest angiosperms, although Ceratophyllum has a long fossilrecord, going back at least 125 mya (Dilcher, 1989 ). Subsequent analyses demonstratedthat this placement was unique to the rbcL data set, but the position of Ceratophyllum,based on evidence from many other genes, is still not clear. It appears as the sister tomonocots in some analyses (e.g., Zanis et al., 2002 ; Davies et al., 2004 ), but furtherwork is needed to identify its proper position.MonocotsAmong extant angiosperms, monocotyledons represent the earliest-appearing majorclade. Using a molecular clock, K. Bremer (2000) dated the origin of the monocot cladeto be 134 mya, older than the oldest angiosperm fossils. Although their exact age isunclear from the fossil record (but see Gandolfo et al., 2002 ), monocots clearlyrepresent an early lineage of angiosperms. There are approximately 52 000 species ofmonocots (Mabberley, 1993 ), representing 22% of all angiosperms. Half of themonocots can be found in the two largest families, Orchidaceae and Poaceae, whichcomprise 34% and 17%, respectively, of all monocots.Phylogenetic studies of nonmolecular data (Donoghue and Doyle, 1989 ; Loconte andStevenson, 1991 ; Doyle and Donoghue, 1992 ) have identified 13 putativesynapomorphies for the monocots, including, among others, a single cotyledon, parallel-veined leaves, sieve cell plastids with several cuneate protein crystals, scattered vascularPlant anatomy, From Wikipedia, the free encyclopedia 53
  • 54. bundles in the stem, and an adventitious root system. An often-overlooked synapomorphyfor monocots is their sympodial growth; although there are other angiosperms withsympodial growth, monocots are nearly exclusively so. These synapomorphies arecovered in detail in the paper by Chase in this issue (2004; see also Judd et al., 2002 ;Soltis et al., in press-b ).Recognition of the monocots as a distinct group within the angiosperms dates from Ray(1703) and was largely based on their possession of a single cotyledon relative to thetwo cotyledons typical of the dicotyledons or "dicots." As reviewed earlier, the lattergroup is now known to be nonmonophyletic, and the term "dicot" should be abandoned.There is, however, a great diversity of form in monocot seedlings (Tillich, 1995 ) andnot all possess an obvious single cotyledon.Another major, distinctive trait of the monocots is their vascular system, which ischaracterized by vascular bundles that are scattered throughout the medulla and cortexand are closed (i.e., do not contain an active cambium; reviewed in Tomlinson, 1995 ).In contrast, basal angiosperms formerly considered dicots (e.g., members of themagnoliid clade) and eudicots possess open vascular bundles arranged in a ring.Another widely cited character of the monocots is their particular form of sieve cellplastids (Behnke, 1969 ), which are triangular with cuneate proteinaceous inclusions.Similar sieve cell plastids are found in Aristolochiaceae (Dahlgren et al., 1985 ). Thissimilarity between monocots and Aristolochiaceae apparently represents convergence, notshared ancestry, because phylogenetic studies of DNA sequences from all three genomes(Qiu et al., 1999 ; Zanis et al., 2002 , 2003 ) have demonstrated a strongly supportedrelationship of Aristolochiaceae to other Piperales within the magnoliid clade.Other traits characteristic of the monocots include parallel venation without free vein-endings (vs. reticulate venation with free vein-endings), intercalary meristem,adventitious roots, and roots without secondary growth. Adventitious roots are foundelsewhere in the angiosperms, in both Piperaceae and Nymphaeaceae.Trimerous flowers have long been considered a uniting feature of the monocots, but it isnot an exclusive one because there are many other basal angiosperms, includingNymphaeaceae and magnoliids, that also exhibit trimery. In fact, character-statereconstructions of the angiosperms indicate that trimery arose early in the angiosperms; itmay be ancestral for all angiosperms except Amborella (Ronse De Craene et al., 2003 ;Zanis et al., 2003 ; Soltis et al., in press-b ), or perhaps all angiosperms, if the shiftaway from trimery in Amborella occurred along the lineage leading to Amborella.Trimery appears, therefore, to be a symplesiomorphic feature for monocots and otherangiosperms and is not a "monocot character."Our understanding of monocot phylogenetics has greatly improved over the past decade,aided greatly by the foci provided by the international monocot symposia held in 1993,1998, and 2003. These meetings have focused attention both on what was known and,more importantly, on which groups needed additional research. As a result, we now knowmore about monocots than any other group of angiosperms of comparable size, a situationthat is remarkable given the paucity of information available in 1985 (Dahlgren et al.,1985 ). This model should be adopted for the other large groups of angiosperms (e.g.,rosids, asterids) so that attention is likewise focused on integration of research programsand gaps in the database.Plant anatomy, From Wikipedia, the free encyclopedia 54
  • 55. There have been several recent analyses of relationships among the monocots, includingthe three-gene analyses of Chase et al. (2000) and D. Soltis et al. (2000) and the seven-gene analysis of Chase et al. (in press ). The first two studies are based on the same threegenes (rbcL, atpB, 18S rDNA); however, Chase et al. (2000) focused only on themonocots and employed a larger number of taxa than used in D. Soltis et al. (2000) .The analysis by Chase et al. (2004) included those three genes, plus partial nuclear 26SrDNA, plastid matK and ndhF, and mitochondrial atpA. The paper in this issue by Chase(2004) provides greater detail on monocot phylogeny, and our coverage will therefore bebrief.All but two molecular phylogenetic analyses of monocots have placed Acorus alone assister to all other monocots. The first exception to this statement was the 18S rDNAanalysis of Bharathan and Zimmer (1995) , in which Acorus was placed outside of themonocots altogether, a result that has to be considered spurious. Combination of 18SrDNA sequence data with sequences from rbcL and atpB (Chase et al., 2000 ; D. Soltiset al., 2000 ) resulted in strong support for the monophyly of monocots, as well as strongsupport for the monophyly of all monocots excluding Acorus. A recent analysis of two ofthe seven genes used in Chase et al. (in press ), rbcL and atpA (Davis et al., in press ),retrieved an alismatid clade that included Acorus. This deviating result is perplexingbecause neither rbcL (Chase et al., 1993 ; Duvall et al., 1993 ) nor atpA (Davis et al.,1998 ) analyzed alone produced such a position for Acorus. In contrast, studies of basalangiosperm relationships that have employed more genes (six to 11) have consistentlyfound Acorus sister to the remaining monocots with strong support (e.g., Qiu et al., 1999 , 2000 ; Zanis et al., 2002 , 2003 ). A recent angiosperm-wide analysis of matKsequence data (Hilu et al., 2003 ), an analysis of ndhF in monocots (Givnish et al., inpress ), and a seven-gene analysis of monocots (Chase et al., in press ) found moderateto strong support for the placement of Acorus as sister to other monocots. Hence, mostanalyses agree on the placement of Acorus as sister to all other monocots.Following Acorus, the monophyly of the remaining monocots is strongly supported.Alismatales are sister to the remaining monocots, which themselves are stronglysupported. Within this remaining large clade are several component subclades:commelinids, Dioscoreales, Petrosaviaceae, Pandanales, Liliales, and Asparagales.Although many of these component subclades receive moderate to strong support,relationships among these subclades have been generally poorly resolved. In the strictconsensus of Chase et al. (2000) , the branching order above Alismatales isDioscoreales, Pandanales, Liliales, and Asparagales + commelinids. The seven-geneanalysis of Chase et al. (in press ) is consistent with this pattern, except thatDioscoreales and Pandanales are sister taxa, and most of these relationships received atleast moderate bootstrap support.ChloranthaceaeChloranthaceae, with their small, simple flowers, have an extensive fossil record, datingback 125 my (e.g., Couper, 1958 ; Walker and Walker, 1984 ; Friis et al., 2000 ).Chloranthaceae are clearly an isolated lineage separate from the magnoliid clade (Fig. 2),but their phylogenetic position remains uncertain. In some analyses (e.g., Zanis et al.,2002 ; Davies et al., 2004 ), they are sister to a clade of magnoliids + eudicots.Relationships and patterns of evolution within Chloranthaceae have been addressed byKong et al. (2002) , Doyle et al. (2003) , Zhang and Renner (2003) , and Eklund et al.(2004) .Plant anatomy, From Wikipedia, the free encyclopedia 55
  • 56. MagnoliidsThe magnoliid clade comprises most of those lineages typically referred to as "primitiveangiosperms" in earlier works (e.g., Stebbins, 1974 ; Cronquist, 1981 , 1988 ;Takhtajan, 1997 ). Although the component families of the magnoliid clade were looselyassociated in previous classifications, for example, as Cronquists (1981) subclassMagnoliidae, relationships among the families and orders were not clear. In addition,Magnoliidae contained groups that are not part of the magnoliid clade as recognized byphylogenetic analyses. Reconstructing relationships within this clade, and evenrecognition of the clade itself, is challenging, given the age of this clade (some putativemembers, such as Archaeanthus, Dilcher and Crane, 1984 , date to the early Cretaceous)and presumably high levels of extinction. Although the major lineages of the magnoliidclade were identified as well-supported clades in earlier studies (e.g., Soltis et al., 1999), composition and interrelationships of the magnoliid clade did not become clear untildata sets of at least five genes for a broad sample of taxa were assembled to address theseproblems (e.g., Qiu et al., 1999 , 2000 ; Zanis et al., 2002 ). Within the magnoliids,Magnoliales and Laurales are sisters, and Piperales and Canellales are sisters (Fig. 2).MagnolialesThis clade comprises six families (Myristicaceae, Degeneriaceae, Himantandraceae,Magnoliaceae, Eupomatiaceae, and Annonaceae), relationships among which are nowclear (e.g., Sauquet et al., 2003 ; Fig. 2). This same clade emerged in the nonmolecularanalysis of Doyle and Endress (2000) . Apparent synapomorphies for the clade includereduced fiber pit borders, stratified phloem, an adaxial plate of vascular tissue in thepetiole, palisade parenchyma, asterosclereids in the leaf mesophyll, continuous tectum inthe pollen, and multiplicative testa in the seed (Doyle and Endress, 2000 ). Furthermore,all members of this clade examined to date have a characteristic deletion in their Apetala3gene (Kim et al., in press ). LauralesLaurales, as currently circumscribed (APG II, 2003 ; see Renner, 1999 ), compriseseven families: Calycanthaceae (including Idiospermaceae), Monimiaceae,Gomortegaceae, Atherospermataceae, Lauraceae, Sipurunaceae, and Hernandiaceae.Amborellaceae and Trimeniaceae have also occasionally been placed in Laurales (e.g.,Cronquist, 1981 , 1988 ); in fact, both Amborella and Trimenia have even beenconsidered part of Monimiaceae (Perkins, 1925 ). Chloranthaceae have also occasionallybeen placed in Laurales (e.g., Thorne, 1974 ; Takhtajan, 1987 , 1997 ). Laurales areunited by a perigynous flower in which the gynoecium is frequently deeply embedded ina fleshy receptacle (Endress and Igersheim, 1997 ; Renner, 1999 ). Other apparentsynapomorphies include the presence of inner staminodia, ascendant ovules, andtracheidal endotesta (Doyle and Endress, 2000 ).PiperalesPrevious circumscriptions of Piperales have varied (e.g., Dahlgren, 1980 ; Cronquist,1981 , 1988 ; Takhtajan, 1987 , 1997 ; Thorne, 1992 ; Heywood, 1993 ), butmolecular studies clearly united Aristolochiaceae, Lactoridaceae, Piperaceae, andSaururaceae (e.g., Qiu et al., 1999 ; Soltis et al., 1999 ; Barkman et al., 2000 ; D.Soltis et al., 2000 ; Zanis et al., 2002 ). In addition, recent studies have placedHydnoraceae, a family of parasitic plants often placed in Rosidae (e.g., Cronquist, 1981; Heywood, 1993 ), within Piperales, although the exact position is not certain ( Nickrentet al., 2002 ). Although not recognized as a group prior to molecular analyses, a numberPlant anatomy, From Wikipedia, the free encyclopedia 56
  • 57. of morphological synapomorphies have been identified: distichous phyllotaxis, a singleprophyll, and oil cells (Doyle and Endress, 2000 ).CanellalesThe sister group of Canellaceae and Winteraceae has been strongly supported in allmultigene analyses (e.g., Qiu et al., 1999 ; Soltis et al., 1999 ; D. Soltis et al., 2000 ;Zanis et al., 2002 , 2003 ), and the clade was obtained in Doyle and Endresss (2000)nonmolecular analysis as well. However, these two families have not typically beenconsidered closely related to each other, and neither was suspected of being related to anymembers of Piperales. For example, Winteraceae have often been considered a closerelative of Magnoliaceae (e.g., Cronquist, 1981 , 1988 ; Heywood, 1993 ), withCanellaceae close to Myristicaceae (e.g., Wilson, 1966 ; Cronquist, 1981 , 1988 ).Furthermore, Winteraceae have often been regarded as perhaps the "most primitive"extant family of angiosperms (Cronquist, 1981 ; Endress, 1986 ). The phylogeneticposition of Winteraceae clearly indicates that the vesselless xylem and plicate carpelsfound in members of the family are secondarily derived (see also Young, 1981 ).Possible synapomorphies for Canellales are a well-differentiated pollen tube transmittingtissue, an outer integument with only two to four cell layers, and seeds with a palisadeexotesta (Doyle and Endress, 2000 ). Additional synapomorphies may include anirregular "first-rank" leaf venation (Hickey and Wolf, 1975 ; Doyle and Endress, 2000), stelar and nodal structure (Keating, 2000 ), and vascularization of the seeds (Deroin,2000 ).EudicotsEudicots comprise approximately 75% of all angiosperm species (Drinnan et al., 1994 )and are strongly supported by molecular data. However, only a single morphologicalsynapomorphy—triaperturate pollen—has been identified. This pollen type is clearlydistinct from the uniaperturate pollen of basal angiosperms, monocots, and all other seedplants, allowing easy assignment of fossil pollen to the eudicots. The fossil pollen recordindicates that the eudicots appeared 125 mya, shortly after the origin of the angiospermsthemselves. The extensive fossil pollen collections worldwide, coupled with solid dates,make it unlikely that the eudicots arose much before this time. Although triaperturatepollen is a synapomorphy for this clade, not all eudicots have triaperturate pollen due tosubsequent changes in pollen structure. The eudicots (referred to instead as tricolpates)are covered in greater detail by Judd and Olmstead (2004) .Basal lineagesA basal grade of five lineages (Ranunculales, Proteales, Sabiaceae, Trochodendraceae,and Buxaceae) subtends the large clade of core eudicots (Hoot et al., 1999 ; D. Soltis etal., 2000 ; Kim et al., 2004 ; Fig. 3). Although Ranunculales are supported as the sisterto all other eudicots, the relative placements of the remaining four lineages of basaleudicots are not clear and require additional study.Plant anatomy, From Wikipedia, the free encyclopedia 57
  • 58. Fig. 3. Summary of phylogenetic relationships among clades of eudicots, based on Hoot et al. (1999) , D. Soltis et al. (2000 , 2003 ), and Kim et al. (2004) View larger version (33K): [in this window] [in a new window]Core eudicotsThe core eudicots comprise the vast majority of eudicot species. Seven major clades(Gunnerales, "Berberidopsidales," Saxifragales, Santalales, Caryophyllales, rosids, andasterids) have been recognized, but the relationships among these clades are not clear(Figs. 1, 3; D. Soltis et al., 2000 ). The topology indicates a rapid radiation, butadditional data are needed to evaluate this hypothesis. Recent studies have identifiedGunnerales as the sister to all other core eudicots (Hilu et al., 2003 ; Soltis et al., 2003). Several important changes in floral genes appear to coincide with the origin of coreeudicots, including duplication of AP3 yielding the euAP3 lineage (Kramer et al., 1998 )and the origin of Apetala1 (Litt and Irish, 2003 ).GunneralesGunnerales comprise two small families, Gunneraceae (Gunnera with approximately 40species) and Myrothamnaceae (Myrothamnus with two species) (or Gunneraceae s.l.sensu APG II, 2003 ). This relationship had not previously been suggested on the basisof morphology because the two genera differ substantially, although molecular supportfor their relationship is very strong. Gunneraceae have a dimerous perianth (Drinnan etal., 1994 ), as do many of the basal eudicot lineages; dimery probably typifies Buxaceae,Trochodendraceae, and Proteaceae (but perhaps not the Platanus lineage) and is commonand perhaps ancestral in Ranunculales (van Tieghem, 1897 ; Drinnan et al., 1994 ;Douglas and Tucker, 1996 ). The placement of Gunnerales as sister to the rest of the coreeudicots implies that the pentamerous perianth typical of most core eudicots was derivedfrom dimerous ancestors (Ronse De Craene et al., 2003 ; Soltis et al., 2003 )."Berberidopsidales"Like Gunnerales, "Berberidopsidales" comprise two small and morphologically disparatefamilies: Berberidopsidaceae (Berberidopsis and Streptothamnus, which is sometimesincluded in Berberidopsis) and Aextoxicaceae (Aextoxicon, one species). Although thisclade has not been recognized at the ordinal level by APG (hence the quotation marks), itis strongly supported by molecular data and is isolated from all other clades. Furthermore,both families have encyclocytic stomata, a rare character and an apparent synapomorphyfor this clade (Soltis et al., in press-b ).Plant anatomy, From Wikipedia, the free encyclopedia 58
  • 59. SaxifragalesSaxifragales are a morphologically eclectic clade of annual and perennial herbs,succulents, aquatics, shrubs, vines, and large trees. Prior to molecular phylogenetics(Morgan and Soltis, 1993 ; Fishbein et al., 2001 ), members of this clade wereclassified in three of Cronquists (1981) six subclasses of dicots (see also Takhtajan,1997 ). Possible synapomorphies for this clade include a partially fused bicarpellategynoecium, a hypanthium, and glandular leaf teeth (Judd et al., 2002 ); aspects of leafvenation and wood anatomy are similar in the woody members of the clade. The bestknown of the 13 families in this clade are Saxifragaceae, Crassulaceae, Grossulariaceae,Paeoniaceae, and Hamamelidaceae. Molecular studies continue to reveal new, unexpectedmembers of this clade, such as Peridiscaceae (Davis and Chase, 2004 ), a family placedin Malpighiales in APG II (2003) .Monophyly of Saxifragales is strongly supported, but the position of this clade relative toother core eudicots remains uncertain. Some analyses have placed it as sister to the rosids,although with weak support (e.g., D. Soltis et al., 2000 ). The simple, pentamerousflowers have long been thought to indicate a relationship with Rosaceae and other rosids,but whether these floral features are synapomorphies for Saxifragales + rosids orsymplesiomorphies (i.e., shared ancestral features) is unclear. Despite the fairly constantgeneral floral structure of Saxifragales, certain aspects of floral evolution within thisclade appear to be quite labile, especially ovary position (e.g., Kuzoff et al., 2001 ).Additional research is needed to resolve the relationship of Saxifragales within the coreeudicots.SantalalesThe seven families of Santalales are united by molecular characters and aspects of theirparasitic habit and are a strongly supported clade of core eudicots. However, relationshipsof Santalales to other core eudicots are not clear, although they occasionally appear nearthe asterids in at least some shortest trees. Furthermore, relationships within this cladehave not yet been resolved, and the monophyly of some of the currently recognizedfamilies has not been supported by molecular evidence. The lack of resolution withinSantalales may be explained in part by apparently rapid rates of molecular evolution in allthree plant genomes (e.g., Nickrent and Starr, 1994 ; Nickrent et al., 1998 ). Aerialhemiparasites (mistletoes) have evolved multiple times in Santalales.CaryophyllalesThe core of Caryophyllales sensu APG II (2003) was considered a closely related groupof families as long ago as the mid-nineteenth century (e.g., Braun, 1864 ; Eichler, 1876 ) and was formally recognized as the Centrospermae by Harms (1934) based onmorphological and embryological characters. Recent molecular studies have identified alarger clade (Caryophyllales sensu APG II) that includes the Caryophyllidae of Cronquist(1981 ; i.e., Caryophyllales, Polygonales, and Plumbaginales) plus a number of familiespreviously considered distantly related to Caryophyllales, including the carnivoroussundews and Venus flytrap (Droseraceae) and Old World pitcher plants (Nepenthaceae).Relationships of Caryophyllales to other core eudicots are not clear, althoughDilleniaceae are sister to Caryophyllales in some analyses, although with low support(e.g., Chase and Albert, 1998 ; D. Soltis et al., 2000 ; Fig. 3), and some shortest treeshave indicated a possible relationship with the asterids. Within Caryophyllales, there aretwo large clades, core and noncore Caryophyllales (Cuénoud et al., 2002 ), thatPlant anatomy, From Wikipedia, the free encyclopedia 59
  • 60. correspond to Caryophyllales and Polygonales sensu Judd et al. (2002) . The coreCaryophyllales clade generally corresponds to Caryophyllales of recent classifications(e.g., Cronquist, 1981 ; Takhtajan, 1997 ) and comprises 19 families, although somecurrently recognized families (e.g., Portulacaceae, Phytolaccaceae) are poly- orparaphyletic and require recircumscription (Cuénoud et al., 2002 ). Synapomorphies forthis clade include unilacunar nodes, stems with concentric rings of xylem and phloem,phloem sieve tubes with plastids with a peripheral ring of proteinaceous filaments and acentral protein crystal, betalains (rather than anthocyanins), loss of the intron in theplastid gene rpl2, a single perianth whorl, free central to basal placentation, an embryocurved around the seed, and presence of perisperm with little or no endosperm (Judd etal., 2002 and references therein). The noncore clade has been identified on the basis ofmolecular data and comprises families classified in Cronquists (1981) Rosidae andDilleniidae. Most surprising is the inclusion in this clade of the carnivorous Droseraceaeand Nepenthaceae. Synapomorphies for the noncore clade are scattered secretory cellscontaining plumbagin, an indumentum of stalked, gland-headed hairs, basal placentation,and starchy endosperm (Judd et al., 2002 ).Many Caryophyllales are adapted to harsh environments, such as high-alkaline soils,high-salt conditions, extreme aridity, and nutrient-poor soils (see descriptions ofcomponent families in Heywood, 1993; Judd et al., 2002 ). Various adaptations, such asCrassulacean acid metabolism and C4 photosynthesis, succulence, carnivory, and saltsecretion, have evolved multiple times (e.g., Juniper et al., 1989 ; Meimberg et al., 2000 ; Pyankov et al., 2001 ; Cameron et al., 2002 ) and have allowed Caryophyllales toexploit these habitats.RosidsThe rosid clade is broader than the traditional subclass Rosidae (Cronquist, 1981 ;Takhtajan, 1980 , 1997 ), also encompassing many families formerly classified in thepolyphyletic subclasses Magnoliidae, Dilleniidae, and Hamamelidae. The rosids comprise140 families and close to one-third of all angiosperm species. Clear synapomorphies forthe rosids have not been identified, although most rosids share several morphological andanatomical features, such as nuclear endosperm development, reticulate pollen exine,generally simple perforations of vessel end-walls, alternate intervessel pitting,mucilaginous leaf epidermis, and two or more whorls of stamens, plus ellagic acid(Hufford, 1992 ; Nandi et al., 1998 ).Relationships within rosids are not clearly resolved. Vitaceae may be sister to the rosids,but this relationship is not strongly supported (Fig. 3; Savolainen et al., 2000a , b ; D.Soltis et al., 2000 ), and Saxifragales may be sister to the Vitaceae + rosids clade, butthis relationship is not strongly supported either (D. Soltis et al., 2000 ). Two largesubclades of rosids, eurosids I (fabids) and II (malvids), have been identified throughmolecular analyses (e.g., Chase et al., 1993 ; Savolainen et al., 2000a , b ; D. Soltis etal., 2000 ; Fig. 1). However, some orders and families (e.g., Crossosomatales,Geraniales, Myrtales) do not fit into either eurosid I or eurosid II. The eurosid I cladecomprises Celastrales, Cucurbitales, Fabales, Fagales, Zygophyllales, Malpighiales,Oxalidales, and Rosales. Of these, Cucurbitales, Fabales, Fagales, and Rosales form the"nitrogen-fixing clade," a clade that contains all angiosperms known to have symbioticrelationships with nodulating nitrogen-fixing bacteria (see D. Soltis et al., 1995 , 1997 ,2000 ). The placements in previous classifications of the species that exhibit thisPlant anatomy, From Wikipedia, the free encyclopedia 60
  • 61. symbiosis indicated that symbiotic relationships with nodulating bacteria must haveoccurred multiple times. Current phylogenetic evidence instead indicates a single originof the predisposition for symbiosis, with perhaps both gains and losses of the symbioticrelationship within the nitrogen-fixing clade itself (Soltis et al., 1995 ; Swensen, 1996). Multiple gains of this association may be more parsimonious than a single gainfollowed by multiple losses (Swensen, 1996 ). The smaller eurosid II clade is composedof Brassicales, Malvales, Sapindales, and Tapisciaceae. Brassicales include allangiosperms known to produce glucosinolates, a form of chemical defense, exceptDrypetes and Putranjiva of the distantly related rosid family Putranjivaceae ofMalpighiales (e.g., Rodman, 1991 ; Rodman et al., 1993 , 1998 ). Previousclassifications led to the conclusion that glucosinolate production had evolved severaltimes in the angiosperms; current phylogenetic evidence indicates instead only two suchorigins. In addition to the large eurosid I and II clades, additional smaller clades havebeen recognized (Crossosomatales, Myrtales, Geraniales, and Picramniaceae), but theirrelationships to each other and to eurosids I and II are not clear. Furthermore,relationships within eurosids I and II are not fully resolved, and much additional work isneeded to reconstruct relationships within the rosid clade. In fact, the rosids represent thelargest remaining problematic group of angiosperms.Several factors may have contributed to the lack of resolution of relationships within therosids. The clade is old, dating at least to the late Santonian to Turonian (approximately84– 89.5 mya; Crepet and Nixon, 1998 ; Magallón et al., 1999 ), and possibly to 94mya, based on an unnamed apparently rosid flower from the Dakota Formation inNebraska (Basinger and Dilcher, 1984 ). Furthermore, molecular-based age estimates ofMyrtales using penalized likelihood (Sanderson, 2002 ) placed the crown radiation ofMyrtales at approximately 110 mya (Sytsma et al., in press ), implying an even older agefor the rosids. The age of the rosid clade is therefore sufficient to have allowed substantialmorphological and molecular diversification and speciation, although the similar age ofthe monocots has not similarly obscured relationships within that clade. The rosid clademay have diversified via a series of radiations (P. Soltis et al., 2004 ), resulting in apattern of polytomies (see Remaining Problems and Future Prospects). Furthermore,subtle nonmolecular features that could potentially unite large groups of families withinthe rosids have not generally been identified because, until the results of molecularanalyses, many families of rosids were not suspected of being closely related, havingbeen placed in four subclasses of dicots (Magnoliidae, Hamamelidae, Dilleniidae, andRosidae), and were therefore not included together in most previous analyses andtreatments. Gaps in morphological data sets across the rosids have likewise made itdifficult to identify synapomorphies for groups of families.AsteridsLike rosids, asterids are a large clade, encompassing nearly one-third of all angiospermspecies (80 000 species) and classified in 114 families (Albach et al., 2001b ). However,unlike the rosids, a group of families corresponding closely to the asterids has beenrecognized on morphological grounds for over 200 years (de Jussieu, 1789 ;Reichenbach, 1828 ; Warming, 1879 ), and several morphological and chemicalfeatures appear to unite all or most asterids. Most notable are iridoid chemical compounds(e.g., Jensen, 1992 ), sympetalous corollas, unitegmic and tenuinucellate ovules, andcellular endosperm development; however, it is still unclear which of these features arePlant anatomy, From Wikipedia, the free encyclopedia 61
  • 62. actually synapomorphies for asterids (cf. Albach et al., 2001a ; Judd et al., 2002 ). Theasterid clade is broader than Asteridae of recent classifications (e.g., Cronquist, 1981 ;Takhtajan, 1980 , 1997 ) and includes also members of the polyphyletic subclassesHamamelidae, Dilleniidae, and Rosidae (Olmstead et al., 1992 , 1993 , 2000 ; Chaseet al., 1993 ; D. Soltis et al., 1997 , 2000 ; Soltis et al., 1999 ; Savolainen et al.,2000a , b ).Many relationships within asterids were resolved by angiosperm-wide analyses, butasterids have also been analyzed in greater detail with extensive taxon sampling and datafrom four (Albach et al., 2001b ) and six (Bremer et al., 2002 ) loci. These studiesconfirmed earlier results of four major clades within asterids (Fig. 1): Cornales are sisterto all other asterids, with Ericales sister to a clade of euasterids I + euasterids II. Thefamilies of Cornales and Ericales were not considered closely related to those ofAsteridae in previous classifications and were placed instead mostly in Rosidae andDilleniidae, respectively. Euasterids are mostly united by flowers with epipetalousstamens that equal the number of corolla lobes and a gynoecium of two fused carpels.Within the euasterids, the euasterid I (or lamiid, Bremer et al., 2002 ) and euasterid II (orcampanulid, Bremer et al., 2002 ) clades are sisters and can be distinguished bothmorphologically and molecularly (Albach et al., 2001b ; Bremer et al., 2001 ; Bremeret al., 2002 ). Most members of euasterids I have opposite leaves, entire leaf margins,hypogynous flowers, "early sympetaly" with a ring-shaped primordium, fusion of stamenfilaments to the corolla tube, and capsular fruits (Bremer et al., 2001 ). The euasterid Iclade comprises Garryales, Gentianales, Solanales, and Lamiales, plus Boraginaceae,Vahliaceae, and Oncothecaceae + Icacinaceae (APG II, 2003 ). Most taxa of euasteridsII have alternate leaves, serrate-dentate leaf margins, epigynous flowers, "late sympetaly"with distinct petal primordia, free stamen filaments, and indehiscent fruits (Bremer et al.,2001 ). It is unclear which of the characters that distinguish euasterids I and II are trulysynapomorphies for these clades and which are symplesiomorphies; both reversals andparallelisms have contributed to complex patterns of morphological evolution in theasterids (Albach et al., 2001a ; Bremer et al., 2001 ). The euasterid II clade iscomposed of Dipsacales, Aquifoliales, Apiales, and Asterales, plus Bruniaceae +Columelliaceae, a small clade of Tribelaceae, Polyosmaceae, Escalloniaceae, andEremosynaceae, and possibly Paracryphiaceae. The euasterid II clade includes familiespreviously classified in Asteridae and Rosidae (Cronquist, 1981 , 1988 ).The supertree approachThe relationships described in this paper are all based on analyses that use the"supermatrix" approach, that is, a taxon-by-character data matrix is assembled andanalyzed, directly producing a tree or set of trees. A problem with this approach is thatcomprehensive data sets become extremely large, and analyses become increasinglycomputationally complex and time-consuming. In addition, different gene sets have notalways sampled the same taxa, requiring assumptions of generic or familial monophyly inthe formation of "mosaic" taxa and/or leading to large amounts of missing data. Analternative to the supermatrix approach is the supertree approach (e.g., Baum, 1992 ;Ragan, 1992 ; Purvis, 1995 ; Ronquist, 1996 ; Bininda-Emonds and Bryant, 1998 ;Sanderson et al., 1998 ), in which trees that overlap in at least a single taxon may bejoined together algorithmically. Although less satisfying than the supermatrix approach inrelating support or conflict for a topology to specific characters, the supertree approach isPlant anatomy, From Wikipedia, the free encyclopedia 62
  • 63. a viable alternative when multiple data sets overlap in only a small fraction of the taxa orwhen the number of taxa to be analyzed is very large. Furthermore, the two approachesseem to give similar results (e.g., Salamin et al., 2002 ).The supertree approach has not been applied extensively to angiosperms, but it offers anopportunity for representation of greater numbers of taxa than the supermatrix analysesconducted to date. A recent supertree analysis combined trees that included allangiosperm families and produced the first comprehensive family-level phylogenetic treefor angiosperms (Davies et al., 2004 ). The basic framework of the angiosperm supertreeis largely consistent with the results of large, multigene analyses of exemplar taxa (e.g.,D. Soltis et al., 2000 ) on which it was based. Amborella is sister to all otherangiosperms, followed by Nymphaeaceae, Austrabaileyales, a clade of monocots +Ceratophyllaceae, Chloranthaceae, and a clade of magnoliids + eudicots. Relationshipswithin monocots, magnoliids, and eudicots are also mostly consistent with the results ofthe supermatrix analyses. This congruence indicates that the placement of those taxa notincluded in the supermatrix analyses may be correct, inasmuch as the data set can convey.Furthermore, some clades that have been difficult to place appear in resolved locations.For example, Caryophyllales are sister to the asterids, and Saxifragales are sister to therosids, positions they occupy in some of the shortest trees obtained in other analyses butnot in the strict consensus trees (e.g., D. Soltis et al., 2000 ). Although the best methodsof supertree construction remain under debate, supertree approaches seem a viablealternative to supermatrix analyses as data sets continue to grow.REMAINING PROBLEMS AND FUTURE PROSPECTSDespite tremendous progress in angiosperm phylogenetics during the past 10 years,several difficult problems remain. Most prominent are (1) relationships among monocots,Chloranthaceae, magnoliids, and eudicots, (2) branching order among basal eudicots, (3)relationships among the major clades of core eudicots, (4) relationships within rosids, (5)relationships of the many lineages of parasitic plants (although this problem has beenaddressed recently by Barkman et al., 2004) , and (6) integration of fossils with extanttaxa into a comprehensive tree of angiosperm phylogeny. Solving these problems willrequire coordinated efforts among angiosperm systematists and paleobotanists and a largeamount of molecular (and other, where appropriate) data.At least some of those nodes that remain poorly resolved (e.g., basal eudicots, coreeudicots, rosids) may be the results of rapid radiations (see P. Soltis et al., 2004 ). If so,increased sampling of molecular characters coupled with inclusion of additional taxa (if aclade has not yet been thoroughly sampled) may help to resolve at least some of theremaining polytomies. For example, the addition of 26S rDNA sequences to the three-gene data set of D. Soltis et al. (2000) for a subset of eudicots provided evidence forGunnerales as the sister to the remaining lineages of core eudicots (D. Soltis et al., 2003), and increased character sampling for data sets of more than 100 taxa improvedrelationships among basal angiosperms (Zanis et al., 2002 ) and within monocots (e.g.,Chase et al., in press). However, if the lack of resolution is due to a true radiation, it maynot be possible to resolve these nodes. Likewise, if poor resolution has resulted from otherfactors, such as extinction, inadequate sampling of extant lineages, ancient reticulation,horizontal gene transfer, or unequal evolutionary rates among lineages, then the prospectsfor resolution, using currently available data and methods of analysis, are also poor.Plant anatomy, From Wikipedia, the free encyclopedia 63
  • 64. Estimates of the age of the angiosperms and the timing of important divergences based onmolecular data do not generally agree with each other (ranging from 125 to >400 mya)or with dates determined from the fossil record (see e.g., Sanderson and Doyle, 2001 ; P.Soltis et al., 2002 ; Sanderson et al., 2004 ). Although most molecular-based ages forangiosperms, and other groups of organisms (e.g., Heckman et al., 2001 ), are mucholder than the fossil record suggests, many recent estimates based on methods that do notassume equal rates of evolutionary change among lineages are similar to, if slightly olderthan, dates inferred from the fossil record (Sanderson et al., 2004 ). Furthermore,estimated ages for specific angiosperm clades are generally older than inferences from thefossil record (e.g., Wikström et al., 2001 , compared with Magallón et al., 1999 ), butthese discrepancies are much smaller than those reported for the age of the angiosperms.However, room for further reconciliation of age estimates inferred from fossils andmolecular data remains. For example, given the numerous diverse fossils reported from asearly as 115–125 mya, perhaps the earliest angiosperms were older than the conservativeestimate of 130 mya. Conversely, molecular methods tend to overestimate ages(Rodríguez-Trelles et al., 2002 ), so refinement of dating approaches is needed tocompensate for this bias.Many of the large clades identified through analysis of molecular data are not easilyrecognized morphologically. Although possible synapomorphies for many clades havebeen proposed by Doyle and Endress (2000) and Judd et al. (2002) , the identificationof nonmolecular synapomorphies is still needed for many clades. This task will requirenew morphological and molecular data for many groups, including both a search for newcharacters and filling in data for many families. Finally, all of this new information—sequences, trees, morphological data—will need to be managed in such a way as to makeit easily accessible to all who are interested via public databases. The development andmaintenance of informatics tools and resources are therefore also major challenges thatlie ahead for angiosperm systematics. Informatics issues may become particularlyimportant as new methods are needed to analyze large amounts of sequence data for moretaxa than have yet been analyzed together and to develop algorithms and methods forconstructing supertrees to link new trees with those that have been archived.The phylogenetic information currently available for angiosperms, and that to come, isfundamentally important for organizing all that is known about the angiosperm branch ofthe tree of life. However, this phylogenetic information is also a prerequisite foraddressing basic questions in a number of other fields, ranging from genomics to ecology. FOOTNOTES1 The authors thank M. Chase, J. Palmer, and an anonymous reviewer for very helpfulcomments on the manuscript. This research was supported in part by NSF grants DEB-0090283 and PGR-0115684.4 psoltis@flmnh.ufl.edu LITERATURE CITEDAlbach D. P. S. Soltis D. E. Soltis 2001a Patterns of embryological and biochemicalevolution in the asterids. Systematic Biology 26: 242-262Plant anatomy, From Wikipedia, the free encyclopedia 64
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  • 76. Other basal lineages include Chloranthaceae, magnoliids, and monocots. Approximatelythree quarters of all angiosperm species belong to the eudicot clade, which is stronglysupported by molecular data but united morphologically by a single synapomorphy—triaperturate pollen. Major clades of eudicots include Ranunculales, which are sister to allother eudicots, and a clade of core eudicots, the largest members of which areSaxifragales, Caryophyllales, rosids, and asterids. Despite rapid progress in resolvingangiosperm relationships, several significant problems remain: (1) relationships amongthe monocots, Chloranthaceae, magnoliids, and eudicots, (2) branching order amongbasal eudicots, (3) relationships among the major clades of core eudicots, (4)relationships within rosids, (5) relationships of the many lineages of parasitic plants, and(6) integration of fossils with extant taxa into a comprehensive tree of angiospermphylogeny.Key Words: Amborella • angiosperms • phylogenyStamen (Redirected from Androecium)For the physician, see Stamen Grigorov.Stamens of the Amaryllis with prominent anthers carrying pollenPlant anatomy, From Wikipedia, the free encyclopedia 76
  • 77. Insects collecting nectar unintentionally transfer pollen to other flowers, causingpollinationThe stamen (plural stamina or stamens, from Latin stamen meaning "thread of thewarp") is the male organ of a flower. Each stamen generally has a stalk called thefilament (from Latin filum, meaning "thread"), and, on top of the filament, an anther(from Ancient Greek anthera, feminine of antheros "flowery," from anthos "flower"),and pollen sacs, called microsporangia. The development of the microsporangia and thecontained haploid gametophytes, (called pollen-grains) is closely comparable with that ofthe microsporangia in gymnosperms or heterosporous ferns. The pollen is set free by theopening (dehiscence) of the anther, generally by means of longitudinal slits, butsometimes by pores, as in the heath family (Ericaceae), or by valves, as in the barberryfamily (Berberidaceae). It is then dropped, or carried by some external agent — wind,water or some member of the animal kingdom — onto the receptive surface of the carpelof the same or another flower, which is thus pollinated.Typical flowers have six stamens inside a perianth (the petals and sepals together),arranged in a whorl around the carpel (pistil). But in some species there are many morethan six present in a flower (see, for example, the spider tree flower, below). Collectively,the stamens are called an androecium (from Greek andros oikia: mans house). They arepositioned just below the gynoecium. The anthers are bilocular, i.e. they have two locules.Each locule contains a microsporangium. The tissue between the locules and the cells iscalled the connective.In an immature, unopened flower bud, the filaments are still short. Their function is thento transport nutrients to the developing pollen. They start to lengthen once the bud opens.The anther can be attached to the filament in two ways: • basifixed : attached at its base to the filament; this gives rise to a longitudinal dehiscence (opening along its length to release pollen) • versatile : attached at its center to the filament; pollen is then released through pores (poricidal dehiscence).Plant anatomy, From Wikipedia, the free encyclopedia 77
  • 78. Scanning electron microscope image of Penta lanceolata anthers, with pollen grains onsurfaceStamens can be connate (fused or joined in the same whorl): • monadelphous : fused into a single, compound structure • diadelphous : joined partially into two androecial structures • synantherous : only the anthers are connate (such as in the Asteraceae)Stamens can also be adnate (fused or joined from more than one whorl): • epipetalous : adnate to the corolla • didynamous : occurring in two pairs of different length • tetradynamos : occurring as a set of six filaments with two shorter ones • exserted : extending beyond the corolla • included : not extending from the corolla.Plant sexuality Main article: Plant sexualityStamen with pollinia and its anther cap. Phalaenopsis orchid.Plant anatomy, From Wikipedia, the free encyclopedia 78
  • 79. In the typical flower (that is, the majority of flowering plant species) each flower has botha pistil and stamens. Bisexual plants are named hermaphrodites or perfect flowers.In some species, however, the flowers are unisexual with only either male or female parts(monoecious = on the same plant; dioecious = on different plants). A flower with onlymale reproductive parts is called androecious. A flower with only female reproductiveparts is called gynoecious.A flower having only functional stamens is called a staminate flower.An abortive or rudimentary stamen is called a staminodium, such as in Scrophularianodosa.The pistil and the stamens of orchids are fused into a column. The top part of the columnis formed by the anther. This is covered by an anther cap.GalleryFlower of the spiderFlowers of wheat atStamens of a daylilyFlowers of the "silk tree"tree (Cratevaanthesis showing(Hemerocallis), (Albizia julibrissin) havereligiosa) with itsstamens. thickly covered in many long thread-likenumerous pollen stamensconspicuous stamensStamens of a passionflower (Passifloracaerulea) showinginteresting symmetryReferences • This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain. Gynoecium Amaryllis style and stigmas A gynoecium (from Ancient Greek gyne, "woman") is the female reproductive part of a flower. The male counterpart is called an androecium. A gynoecium is composed of one or more pistils. A pistil may consist of a single free carpel, or be formed from a number of carpels that are fused. The pistil itself is formed from the stigma, style, and ovary.Plant anatomy, From Wikipedia, the free encyclopedia 79
  • 80. A plant ovary (much like an animal ovary) is the part of the pistil which contains ovules.The style is generally referred to as stalklike, without ovules located between the ovary(at the bottom of the pistil) and the stigma (located at the top portion of the pistil). Insome plant species styles are not found in the pistils. Stigma is the pollen receptor withinthe pistil at the top of the pistil. Stigmas may be discretely defined structures or they maybe within a region referred to as the stigmatic region. [1]Pistils or ovaries can be either simple meaning only one carpel or compound meaningtwo or more carpels.[1]Contents • 1 Carpel anatomy • 2 The pistil o 2.1 Inferior vs. superior ovaries o 2.2 The ovule • 3 ReferencesCarpel anatomy A large stigma with anthers visible in the background A carpel is the basic unit of the female reproductive organ of a flower, the gynoecium. A flower may have zero, one, or more carpels. Multiple carpels may combine into a single pistil, or into multiple pistils. The parts of the carpel are: • the stigma (from Ancient Greek stigma "mark, puncture"), usually the terminal (end) portion that receives the pollen (male gametophytes); it is commonly somewhat glutinous or viscid; • the style (from Latin stilus "stake, stylus"), a stalk connecting the stigma with the ovary below containing the transmitting tract, which facilitates the growth of the pollen tube and hence the movement of the male gamete to the ovule; and • the ovary (from Latin ovum "egg") or megasporophyll (see sporophyll) containing the female reproductive cell or ovule.The pistil This article or section is in need of attention from an expert on the subject. WikiProject Plants or the Plants Portal may be able to help recruit one. If a more appropriate WikiProject or portal exists, please adjust this template accordingly.Plant anatomy, From Wikipedia, the free encyclopedia 80
  • 81. Flowers and fruit (capsules) of the ground orchid, Spathoglottis plicata, illustrating aninferior ovary.A pistil (from Latin pistillum "pestle") is made up of a carpel (if single) or carpels (iffused). A gynoecium that consists of a single free carpel is termed monocarpous. Thatwith two or more fused carpels (called a compound ovary or compound pistil) is termedsyncarpous. However, if the gynoecium consists of one or more free, simple, and distinctcarpels, each carpel makes an individual pistil and the gynoecium is termed apocarpous.Fertilization of the ovule or ovules results in development of the carpel(s) into a fruit.When two or more carpels are fused or joined together its called syncarpy. In acompound pistil, the carpels are fused together in one of two basic ways: • the carpels are fused at or near their margins (parietal placentation), usually forming a single large cavity — an example would be the violet. • the folded carpels extend in towards the center, being fused along their outer faces (laterally concrescent), with the placentae arranged around a central column of tissue (axile placentation). There may be as many locules as there are carpels; and tissue of the receptacle may be involved in forming the axillary column. An example of axile placentation would be the lily.A complicating factor in all of this is the fact that in some species syncarpy is presentonly at the base of the carpels, the pistil being apocarpous in the upper part. The mannerof fusing of the carpels can also vary from one part of the pistil to another.Inferior vs. superior ovariesThe gynoecium, the collective term for all the carpels, is the innermost whorl of the partsof a flower, and in many flowers the other parts (sepals, petals, and stamens) are attachedto the receptacle beneath the gynoecium. In such cases, where the ovary lies above theattachments of the other distinct floral parts, the flower is described as hypogynous or ashaving a superior ovary. In some species (examples include plum, cherry, andblackberry), the other (noncarpellary) floral parts are fused to form a cup called a floraltube or hypanthium. In these flowers, the ovary lies physically lower than the lobes ofthe sepals and petals and below the point of attachment of the stamen filaments — theovary is still considered to be superior but the flower is termed perigynous.In those flowers in which the floral tube is fused with the ovary, the sepals, petals, andstamens appear to grow out from the top of the ovary, and the flower is said to beepigynous and have an inferior ovary. Examples of plant families with inferior ovariesPlant anatomy, From Wikipedia, the free encyclopedia 81
  • 82. include orchid, sunflower, and cactus. The position of the ovary is an importantconsideration in the identification and classification of plant species, as well as the kindof fruit that develops after fertilization.The ovule Main article: OvuleLongitudinal section of female flower of squash showing ovary, ovules, pistil, and petalsThe ovule (from Latin ovulum "small egg"), which represents the megasporangium,when mature, consists of one or two coats surrounding the central nucellus, except at theapex where an opening, the micropyle, is left. The nucellus is a cellular tissue envelopingone large cell, the embryo-sac or megaspore. The germination of the megaspore consistsin the repeated division of its nucleus to form two groups of four, one group at each endof the embryo-sac. One nucleus from each group, the polar nucleus, passes to the centreof the sac, where the two fuse to form the so-called definitive nucleus. Of the three cellsat the micropylar end of the sac, all naked cells (the so-called egg-apparatus), one is theegg-cell or oosphere, the other two, which may be regarded as representing abortive egg-cells (in rare cases capable of fertilization), are known as synergidae. The three cells atthe opposite end are known as antipodal cells and become invested with a cell-wall.The carpel of a simple apocarpous gynoecium appears as a folded structure,differentiated into a basal fertile part (ovary) and an upper sterile part (style). Variousinterpretations of the origin from a leaf-like structure have been made (Esau, 1965), butthe important anatomical description is that of a variously folded tissue surrounding acavity (called a locule) within which projects one or more ovules, attached by or along aplacenta. Typically, a carpel has two placentae. An example of a simple carpel is that ofa pea, bean or Arabidopsis: the fruit develops from the single carpel consisting of tworows of ovules aligned beside one another along the placental margin.References • Esau, K. 1965. Plant Anatomy, 2nd Edition. John Wiley & Sons. 767 pp. • This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.LeafFor other uses, see Leaf (disambiguation)."Foliage" redirects here. For fall foliage, see Autumn leaf color.Plant anatomy, From Wikipedia, the free encyclopedia 82
  • 83. The leaves of a Beech treeA leaf with laminar structure and pinnate venationVein skeleton of a leafIn botany, a leaf is an above-ground plant organ specialized for photosynthesis. For thispurpose, a leaf is typically flat (laminar) and thin, to expose the cells containingchloroplast to light over a broad area, and to allow light to penetrate fully into the tissues.Leaves are also the sites in most plants where transpiration and guttation take place.Leaves can store food and water, and are modified in some plants for other purposes. Thecomparable structures of ferns are correctly referred to as fronds. Furthermore, leaves areprominent in the human diet as leaf vegetables.Plant anatomy, From Wikipedia, the free encyclopedia 83
  • 84. Contents • 1 Leaf anatomy o 1.1 Epidermis o 1.2 Mesophyll o 1.3 Veins • 2 Leaf morphology o 2.1 Basic leaf types o 2.2 Arrangement on the stem o 2.3 Divisions of the lamina (blade) o 2.4 Characteristics of the petiole o 2.5 Venation (arrangement of the veins) o 2.6 Leaf morphology changes within a single plant • 3 Leaf terminology o 3.1 Shape o 3.2 Margins (edge) o 3.3 Tip of the leaf o 3.4 Base of the leaf o 3.5 Surface of the leaf o 3.6 Hairiness (trichomes) • 4 Adaptations • 5 Interactions with other organisms • 6 Bibliography • 7 Footnotes • 8 See also • 9 External linksLeaf anatomyA structurally complete leaf of an angiosperm consists of a petiole (leaf stem), a lamina(leaf blade), and stipules (small processes located to either side of the base of the petiole).The petiole attaches to the stem at a point called the "leaf axil". Not every speciesproduces leaves with all of the aforementioned structural components. In some species,paired stipules are not obvious or are absent altogether. A petiole may be absent, or theblade may not be laminar (flattened). The tremendous variety shown in leaf structure(anatomy) from species to species is presented in detail below under Leaf morphology.After a period of time (i.e. seasonally, during the autumn), deciduous trees shed theirleaves. These leaves then decompose into the soil.A leaf is considered a plant organ and typically consists of the following tissues: 1. An epidermis that covers the upper and lower surfaces 2. An interior chlorenchyma called the mesophyll 3. An arrangement of veins (the vascular tissue).Plant anatomy, From Wikipedia, the free encyclopedia 84
  • 85. EpidermisSEM image of Nicotiana alata leafs epidermis, showing trichomes (hair-likeappendages) and stomata (eye-shaped slits, visible at full resolution).The epidermis is the outer multi-layered group of cells covering the leaf. It forms theboundary separating the plants inner cells from the external world. The epidermis servesseveral functions: protection against water loss, regulation of gas exchange, secretion ofmetabolic compounds, and (in some species) absorption of water. Most leaves showdorsoventral anatomy: the upper (adaxial) and lower (abaxial) surfaces have somewhatdifferent construction and may serve different functions.The epidermis is usually transparent (epidermal cells lack chloroplasts) and coated on theouter side with a waxy cuticle that prevents water loss. The cuticle is in some casesthinner on the lower epidermis than on the upper epidermis, and is thicker on leaves fromdry climates as compared with those from wet climates.The epidermis tissue includes several differentiated cell types: epidermal cells, guardcells, subsidiary cells, and epidermal hairs (trichomes). The epidermal cells are the mostnumerous, largest, and least specialized. These are typically more elongated in the leavesof monocots than in those of dicots.The epidermis is covered with pores called stomata, part of a stoma complex consistingof a pore surrounded on each side by chloroplast-containing guard cells, and two to foursubsidiary cells that lack chloroplasts. The stoma complex regulates the exchange ofPlant anatomy, From Wikipedia, the free encyclopedia 85
  • 86. gases and water vapor between the outside air and the interior of the leaf. Typically, thestomata are more numerous over the abaxial (lower) epidermis than the adaxial (upper)epidermis.MesophyllMost of the interior of the leaf between the upper and lower layers of epidermis is aparenchyma (ground tissue) or chlorenchyma tissue called the mesophyll (Greek for"middle leaf"). This assimilation tissue is the primary location of photosynthesis in theplant. The products of photosynthesis are called "assimilates".Fallen leaves at autumn.In ferns and most flowering plants the mesophyll is divided into two layers: • An upper palisade layer of tightly packed, vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis. Its cells contain many more chloroplasts than the spongy layer. These long cylindrical cells are regularly arranged in one to five rows. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. This separation must be minimal to afford capillary action for water distribution. In order to adapt to their different environment (such as sun or shade), plants had to adapt this structure to obtain optimal result. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil, are single-layered. • Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more rounded and not so tightly packed. There are large intercellular air spaces. These cells contain fewer chloroplasts than those of the palisade layer.The pores or stomata of the epidermis open into substomatal chambers, connecting to airspaces between the spongy layer cells.These two different layers of the mesophyll are absent in many aquatic and marsh plants.Even an epidermis and a mesophyll may be lacking. Instead for their gaseous exchangesthey use a homogeneous aerenchyma (thin-walled cells separated by large gas-filledspaces). Their stomata are situated at the upper surface.Leaves are normally green in color, which comes from chlorophyll found in plastids inthe chlorenchyma cells. Plants that lack chlorophyll cannot photosynthesize.Plant anatomy, From Wikipedia, the free encyclopedia 86
  • 87. Autumn LeavesFallen autumn leavesLeaves in temperate, boreal, and seasonally dry zones may be seasonally deciduous(falling off or dying for the inclement season). This mechanism to shed leaves is calledabscission. After the leaf is shed, a leaf scar develops on the twig. In cold autumns theysometimes change color, and turn yellow, bright orange or red as various accessorypigments (carotenoids and xanthophylls) are revealed when the tree responds to cold andreduced sunlight by curtailing chlorophyll production. Red anthocyanin pigments arenow thought to be produced in the leaf as it dies.VeinsThe veins are the vascular tissue of the leaf and are located in the spongy layer of themesophyll. They are typical examples of pattern formation through ramification. Thepattern of the veins is called venation.The veins are made up of: • xylem, tubes that brings water and minerals from the roots into the leaf. • phloem, tubes that usually moves sap, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf.The xylem typically lies over the phloem. Both are embedded in a dense parenchymatissue, called "pith", with usually some structural collenchyma tissue present.Leaf morphologyUnderside view of a leafExternal leaf characteristics (such as shape, margin, hairs, etc.) are important foridentifying plant species, and botanists have developed a rich terminology for describingleaf characteristics. These structures are a part of what makes leaves determinant; theygrow and achieve a specific pattern and shape, then stop. Other plant parts like stems orroots are non-determinant, and will usually continue to grow as long as they have theresources to do so.Classification of leaves can occur through many different designative schema, and thetype of leaf is usually characteristic of a species, although some species produce morePlant anatomy, From Wikipedia, the free encyclopedia 87
  • 88. than one type of leaf. The longest type of leaf is a leaf from palm trees, measuring at ninefeet long. The terminology associated with the description of leaf morphology ispresented, in illustrated form, at Wikibooks.Basic leaf typesLeaves of the White Spruce (Picea glauca) are needle-shaped and their arrangement isspiral • Ferns have fronds. • Conifer leaves are typically needle-, awl-, or scale-shaped • Angiosperm (flowering plant) leaves: the standard form includes stipules, a petiole, and a lamina. • Lycophytes have microphyll leaves. • Sheath leaves (type found in most grasses). • Other specialized leaves (such as those of Nepenthes)Arrangement on the stemDifferent terms are usually used to describe leaf placement (phyllotaxis):The leaves on this plant are arranged in pairs opposite one another, with successive pairsat right angles to each other ("decussate") along the red stem. Note developing buds inthe axils of these leaves. • Alternate — leaf attachments are singular at nodes, and leaves alternate direction, to a greater or lesser degree, along the stem. • Opposite — leaf attachments are paired at each node; decussate if, as typical, each successive pair is rotated 90° progressing along the stem; or distichous if not rotated, but two-ranked (in the same geometric flat-plane). • Whorled — three or more leaves attach at each point or node on the stem. As with opposite leaves, successive whorls may or may not be decussate, rotated byPlant anatomy, From Wikipedia, the free encyclopedia 88
  • 89. half the angle between the leaves in the whorl (i.e., successive whorls of three rotated 60°, whorls of four rotated 45°, etc). Opposite leaves may appear whorled near the tip of the stem. • Rosulate — leaves form a rosetteAs a stem grows, leaves tend to appear arranged around the stem in a way that optimizesyield of light. In essence, leaves form a helix pattern centred around the stem, eitherclockwise or counterclockwise, with (depending upon the species) the same angle ofdivergence. There is a regularity in these angles and they follow the numbers in aFibonacci sequence: 1/2, 2/3, 3/5, 5/8, 8/13, 13/21, 21/34, 34/55, 55/89. This series tendsto a limit of 360° x 34/89 = 137.52 or 137° 30, an angle known mathematically as thegolden angle. In the series, the numerator indicates the number of complete turns or"gyres" until a leaf arrives at the initial position. The denominator indicates the numberof leaves in the arrangement. This can be demonstrated by the following: • alternate leaves have an angle of 180° (or 1/2) • 120° (or 1/3) : three leaves in one circle • 144° (or 2/5) : five leaves in two gyres • 135° (or 3/8) : eight leaves in three gyres.Divisions of the lamina (blade)Two basic forms of leaves can be described considering the way the blade is divided. Asimple leaf has an undivided blade. However, the leaf shape may be formed of lobes, butthe gaps between lobes do not reach to the main vein. A compound leaf has a fullysubdivided blade, each leaflet of the blade separated along a main or secondary vein.Because each leaflet can appear to be a simple leaf, it is important to recognize where thepetiole occurs to identify a compound leaf. Compound leaves are a characteristic of somefamilies of higher plants, such as the Fabaceae. The middle vein of a compound leaf or afrond, when it is present, is called a rachis. • Palmately compound leaves have the leaflets radiating from the end of the petiole, like fingers off the palm of a hand, e.g. Cannabis (hemp) and Aesculus (buckeyes). • Pinnately compound leaves have the leaflets arranged along the main or mid-vein. o odd pinnate: with a terminal leaflet, e.g. Fraxinus (ash). o even pinnate: lacking a terminal leaflet, e.g. Swietenia (mahogany). • Bipinnately compound leaves are twice divided: the leaflets are arranged along a secondary vein that is one of several branching off the rachis. Each leaflet is called a "pinnule". The pinnules on one secondary vein are called "pinna"; e.g. Albizia (silk tree). • trifoliate: a pinnate leaf with just three leaflets, e.g. Trifolium (clover), Laburnum (laburnum). • pinnatifid: pinnately dissected to the midrib, but with the leaflets not entirely separate, e.g. Polypodium, some Sorbus (whitebeams).Plant anatomy, From Wikipedia, the free encyclopedia 89
  • 90. Characteristics of the petioleThe overgrown petioles of Rhubarb (Rheum rhabarbarum) are edible.Petiolated leaves have a petiole. Sessile leaves do not: the blade attaches directly to thestem. In clasping or decurrent leaves, the blade partially or wholly surrounds the stem,often giving the impression that the shoot grows through the leaf. When this is actuallythe case, the leaves are called "perfoliate", such as in Claytonia perfoliata. In peltateleaves, the petiole attaches to the blade inside from the blade margin.In some Acacia species, such as the Koa Tree (Acacia koa), the petioles are expanded orbroadened and function like leaf blades; these are called phyllodes. There may or may notbe normal pinnate leaves at the tip of the phyllode.A stipule, present on the leaves of many dicotyledons, is an appendage on each side at thebase of the petiole resembling a small leaf. Stipules may be lasting and not be shed (astipulate leaf, such as in roses and beans), or be shed as the leaf expands, leaving a stipulescar on the twig (an exstipulate leaf). • The situation, arrangement, and structure of the stipules is called the "stipulation". o free o adnate : fused to the petiole base o ochreate : provided with ochrea, or sheath-formed stipules, e.g. rhubarb, o encircling the petiole base o interpetiolar : between the petioles of two opposite leaves. o intrapetiolar : between the petiole and the subtending stemVenation (arrangement of the veins)Palmate-veined leafPlant anatomy, From Wikipedia, the free encyclopedia 90
  • 91. Vein skeleton of a Hydrangea leafThere are two subtypes of venation, namely, craspedodromous, where the major veinsstretch up to the margin of the leaf, and camptodromous, when major veins extend closeto the margin, but bend before they intersect with the margin. • Feather-veined, reticulate — the veins arise pinnately from a single mid-vein and subdivide into veinlets. These, in turn, form a complicated network. This type of venation is typical for (but by no means limited to) dicotyledons. o Pinnate-netted, penniribbed, penninerved, penniveined; the leaf has usually one main vein (called the mid-vein), with veinlets, smaller veins branching off laterally, usually somewhat parallel to each other; eg Malus (apples). o Three main veins branch at the base of the lamina and run essentially parallel subsequently, as in Ceanothus. A similar pattern (with 3-7 veins) is especially conspicuous in Melastomataceae. o Palmate-netted, palmate-veined, fan-veined; several main veins diverge from near the leaf base where the petiole attaches, and radiate toward the edge of the leaf; e.g. most Acer (maples). • Parallel-veined, parallel-ribbed, parallel-nerved, penniparallel — veins run parallel for the length of the leaf, from the base to the apex. Commissural veins (small veins) connect the major parallel veins. Typical for most monocotyledons, such as grasses. • Dichotomous — There are no dominant bundles, with the veins forking regularly by pairs; found in Ginkgo and some pteridophytes.Note that although it is the more complex pattern, branching veins appear to beplesiomorphic and in some form were present in ancient seed plants as long as 250million years ago. A pseudo-reticulate venation that is actually a highly modifiedpenniparallel one is an autapomorphy of some Melanthiaceae which are monocots, e.g.Paris quadrifolia (True-lovers Knot).Leaf morphology changes within a single plant • Homoblasty - Characteristic in which a plant has small changes in leaf size, shape, and growth habit between juvenile and adult stages. • Heteroblasty - Charactistic in which a plant has marked changes in leaf size, shape, and growth habit between juvenile and adult stages.Plant anatomy, From Wikipedia, the free encyclopedia 91
  • 92. Leaf terminologyChart illustrating some leaf morphology termsShape Main article: Leaf shapeMargins (edge)The leaf margin is characteristic for a genus and aids in determining the species. • entire: even; with a smooth margin; without toothing • ciliate: fringed with hairs • crenate: wavy-toothed; dentate with rounded teeth, such as Fagus (beech) • dentate: toothed, such as Castanea (chestnut) o coarse-toothed: with large teeth o glandular toothed: with teeth that bear glands. • denticulate: finely toothed • doubly toothed: each tooth bearing smaller teeth, such as Ulmus (elm) • lobate: indented, with the indentations not reaching to the center, such as many Quercus (oaks) o palmately lobed: indented with the indentations reaching to the center, such as Humulus (hop).Plant anatomy, From Wikipedia, the free encyclopedia 92
  • 93. • serrate: saw-toothed with asymmetrical teeth pointing forward, such as Urtica (nettle) • serrulate: finely serrate • sinuate: with deep, wave-like indentations; coarsely crenate, such as many Rumex (docks) • spiny: with stiff, sharp points, such as some Ilex (hollies) and Cirsium (thistles).Tip of the leafLeaves showing various morphologies. Clockwise from upper left: tripartite lobation,elliptic with serrulate margin, peltate with palmate venation, acuminate odd-pinnate(center), pinnatisect, lobed, elliptic with entire margin • acuminate: long-pointed, prolonged into a narrow, tapering point in a concave manner. • acute: ending in a sharp, but not prolonged point • cuspidate: with a sharp, elongated, rigid tip; tipped with a cusp. • emarginate: indented, with a shallow notch at the tip.Plant anatomy, From Wikipedia, the free encyclopedia 93
  • 94. • mucronate: abruptly tipped with a small short point, as a continuation of the midrib; tipped with a mucro. • mucronulate: mucronate, but with a smaller spine. • obcordate: inversely heart-shaped, deeply notched at the top. • obtuse: rounded or blunt • truncate: ending abruptly with a flat end, that looks cut off.Base of the leaf • acuminate: coming to a sharp, narrow, prolonged point. • acute: coming to a sharp, but not prolonged point. • auriculate: ear-shaped • cordate: heart-shaped with the notch towards the stalk. • cuneate: wedge-shaped. • hastate: shaped like an halberd and with the basal lobes pointing outward. • oblique: slanting. • reniform: kidney-shaped but rounder and broader than long. • rounded: curving shape. • sagittate: shaped like an arrowhead and with the acute basal lobes pointing downward. • truncate: ending abruptly with a flat end, that looks cut off.Surface of the leafScale-shaped leaves of a Norfolk Island Pine, Araucaria heterophylla.The surface of a leaf can be described by several botanical terms: • farinose: bearing farina; mealy, covered with a waxy, whitish powder. • glabrous: smooth, not hairy. • glaucous: with a whitish bloom; covered with a very fine, bluish-white powder. • glutinous: sticky, viscid. • papillate, papillose: bearing papillae (minute, nipple-shaped protuberances). • pubescent: covered with erect hairs (especially soft and short ones) • punctate: marked with dots; dotted with depressions or with translucent glands or colored dots.Plant anatomy, From Wikipedia, the free encyclopedia 94
  • 95. • rugose: deeply wrinkled; with veins clearly visible. • scurfy: covered with tiny, broad scalelike particles. • tuberculate: covered with tubercles; covered with warty prominences. • verrucose: warted, with warty outgrowths. • viscid, viscous: covered with thick, sticky secretions.The leaf surface is also host to a large variety of microorganisms; in this context it isreferred to as the phyllosphere.Hairiness (trichomes)Common Mullein (Verbascum thapsus) leaves are covered in dense, stellate trichomes.Scanning electron microscope image of trichomes on the lower surface of a Coleusblumei [coleus] leaf."Hairs" on plants are properly called trichomes. Leaves can show several degrees ofhairiness. The meaning of several of the following terms can overlap. • glabrous: no hairs of any kind present. • arachnoid, arachnose: with many fine, entangled hairs giving a cobwebby appearance. • barbellate: with finely barbed hairs (barbellae). • bearded: with long, stiff hairs. • bristly: with stiff hair-like prickles.Plant anatomy, From Wikipedia, the free encyclopedia 95
  • 96. • canescent: hoary with dense grayish-white pubescence. • ciliate: marginally fringed with short hairs (cilia). • ciliolate: minutely ciliate. • floccose: with flocks of soft, woolly hairs, which tend to rub off. • glandular: with a gland at the tip of the hair. • hirsute: with rather rough or stiff hairs. • hispid: with rigid, bristly hairs. • hispidulous: minutely hispid. • hoary: with a fine, close grayish-white pubescence. • lanate, lanose: with woolly hairs. • pilose: with soft, clearly separated hairs. • puberulent, puberulous: with fine, minute hairs. • pubescent: with soft, short and erect hairs. • scabrous, scabrid: rough to the touch • sericeous: silky appearance through fine, straight and appressed (lying close and flat) hairs. • silky: with adpressed, soft and straight pubescence. • stellate, stelliform: with star-shaped hairs. • strigose: with appressed, sharp, straight and stiff hairs. • tomentose: densely pubescent with matted, soft white woolly hairs. o cano-tomentose: between canescent and tomentose o felted-tomentose: woolly and matted with curly hairs. • villous: with long and soft hairs, usually curved. • woolly: with long, soft and tortuous or matted hairs.Adaptations This article or section seems to contain embedded lists that may require cleanup. To meet Wikipedias style guidelines, please help improve this article by: removing items which are not notable, encyclopedic, or helpful from the list(s); incorporating appropriate items into the main body of the article; and discussing this issue on the talk page.Poinsettia bracts are leaves which have evolved red pigmentation in order to attractinsects and birds to the central flowers, an adaptive function normally served by petals(which are themselves highly modified leaves).In the course of evolution, leaves adapted to different environments in the followingways:Plant anatomy, From Wikipedia, the free encyclopedia 96
  • 97. • A certain surface structure avoids moistening by rain and contaminations (Lotus effect). • Sliced leaves reduce wind resistance. • Hairs on the leaf surface trap humidity in dry climates and creates a large boundary layer and reduces water loss. • Waxy leaf surfaces reduce water loss. • Shiny leaves deflect the suns rays. • Reductions of leaf sizes accompanied by a transfer of the photosynthetic functions to the stems reduces water loss. • In more or less opaque or buried in the soil leaves translucent windows filter the light before the photosynthetis takes place at the inner leaf surfaces (e.g. Fenestraria). • Thicker leaves store water (leaf succulents). • Aromatic oils, poisons or pheromones produced by leaf borne glands deter herbivores (e.g. eucalypts). • Inclusions of crystalline minerals deters herbivores. • A transformation into petals attracts pollinators. • A transformation into spines protects the plants (e.g. cactus). • A transformation into insect traps helps feeding the plants (carnivorous plants). • A transformation into bulbs helps storing food and water (e.g. onion). • A transformation into tendrils allow the plant to climb (e.g. pea). • A transformation into bracts and pseudanthia (false flowers) replaces normal flower structures if the true flowers are extremely reduced (e.g. Spurges).Interactions with other organismsPlant anatomy, From Wikipedia, the free encyclopedia 97
  • 98. Leaf insects mimic leaves.Although not as nutritious as other organs such as fruit, leaves provide a food source formany organisms. Animals which eat leaves are known as folivores. The leaf is one of themost vital parts of the plant, and plants have evolved protection against folivores such astannins, chemicals which hinder the digestion of proteins and have an unpleasant taste.Some animals have cryptic adaptations to avoid their own predators, for example somecaterpillars will create a small home in the leaf by folding it over themselves, while otherherbivores and their prey mimic the appearance of the leaf. Some insects, such as thekatydid, take this even further, moving from side to side much like a leaf does in thewind.Bibliography • Leaves: The formation, charactistics and uses of hundred of leaves in all parts of the world by Ghillean Tolmie Prance. 324 photographic plates in black and white, and colour by Kjell B Sandved 256 pages[1]Footnotes 1. ^ Published by Thames and Hudson (London) with an ISBN 0 500 54104 3See also • Abscission (losing of leaves) • Cladophyll • Guttation (beads of fluid forming at leaf margins) • Leaf area index • Phylloclade • Vernation (sprouting of leaves) • Evolution of leaves This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (September 2007)External links Wikimedia Commons has media related to: LeavesLook up leaf inWiktionary, the free dictionary. • VASCULAR PLANT SYSTEMATICS Section B. General Characters and Character States: Position and Arrangement • Science aid: Leaf Leaf structure and transpiration resource for teens.AbscissionPlant anatomy, From Wikipedia, the free encyclopedia 98
  • 99. Abscission (from Latin abscindere, from ab- ‘off, away’ + scindere ‘to cut’) is theshedding of a body part. It most commonly refers to the process by which a plantintentionally drops one or more of its parts, such as a leaf, fruit, flower or seed, thoughthe term is also used to describe the shedding of a claw by an animal.Contents • 1 Use • 2 Types • 3 Hormone involvement • 4 External linksUseA plant will abscise a part either to discard a member that is no longer necessary, such asa leaf during autumn, or a flower following fertilisation, or for the purposes ofreproduction. Most deciduous plants drop their leaves by abscission before winter, whileevergreen plants continuously abscise their leaves. Another form of abscission is fruitdrop, when a plant abscises fruit while still immature, in order to conserve resourcesneeded to bring the remaining fruit to maturity. If a leaf is damaged a plant may alsoabscise it to conserve water or photosynthetic efficiency, depending on the costs to theplant as a whole.TypesIn deciduous trees, an abscission zone, also called a separation zone, is formed at the baseof the petiole. It is composed of a top layer which has cells with weak walls, and a bottomlayer which expands in the autumn, breaking the weak walls of the cells in the top layer.This allows the leaf to be shed.In woody plants, an abscission layer is formed composed of parenchyma cells boundedon both sides with cork. This layer is found at the base of the leaf petioles in woodyangiosperms and gymnosperms and because of the disintegration of the parenchymalayer, the organ, such as a leaf or bark, is separated from the parent plant. Abscission is anatural process of plant growth induced by the plant, in contrast to decaying or falling offdue to other causes.The liberation of a fungal spore by the withering away of an adjoining layer is also calledabscission.Hormone involvementThe gaseous plant hormone ethylene can stimulate abscission. While researchersoriginally believed abscisic acid to be the hormone that stimulated abscission (for whichthe hormone was named), it was later proven that it does not play a primary role.[citationneeded]Auxin is a plant hormone which can prevent the formation of abscission layers andpremature fruit drop. Auxin is also believed to play a part in the shedding of leaves andtheir autumn color change. This happens due to continuous release of auxin in a youngleaf; however, as leaves gets old and auxin supply dwindles, an abscission layer formsand leaves shed. In woody plants preparing to shed their leaves, the abscission zone orlayer cuts off the movement of auxin from the leaf blade to the leaf.[citation needed]External links-Nikon MicroscopyUPlant anatomy, From Wikipedia, the free encyclopedia 99
  • 100. CladophyllCladophylls also called cladodes are photosynthetic branches or portions of a stem thatresemble and function as a leaf, as in the asparagus. Cladophylls are flattened, modifiedstems that resemble leaves, many cacti (especially Opuntia) and structurally similarplants have cladophylls.GuttationGuttation on a EquisetumGuttation on a strawberry leafGuttation on a prayer plantGuttation is the appearance of drops of xylem sap on the tips or edges of leaves of somevascular plants, such as grasses.At night, transpiration usually does not occur because most plants have their stomataclosed. When there is a high soil moisture level, water will enter plant roots, because thePlant anatomy, From Wikipedia, the free encyclopedia 100
  • 101. water potential of the roots is lower than in the soil solution. The water will accumulatein the plant creating a slight root pressure. The root pressure forces some water to exudethrough special leaf tip or edge structures, hydathodes, forming drops. Root pressureprovides the impetus for this flow, rather than transpirational pull.Guttation fluid may contain a variety of organic compounds, mainly sugars, and mineralnutrients, and potassium.[1] On drying, a white crust remains on the leaf surface.If high levels of nitrogen appear in the fluid, then that is a sign of fertilizer burn. Excessnitrogen must be leached from the soil by addition of large quantities of water. This mayresult in water pollution, but is the best way to restore soil fertility.[2]Guttation is not to be confused with dew, which condenses from the atmosphere onto theplant surface.See also • Soil plant atmosphere continuumReferences 1. ^ Goatley, James L.; Lewis, Ralph W. (March 1966). "Composition of Guttation Fluid from Rye, Wheat, and Barley Seedlings". Plant Physiology 41 (3): 373–375. PMID 16656266. Retrieved on 2006-10-31. 2. ^ Avoiding Fertilizer BurnLeaf Area Index (Redirected from Leaf area index)The Leaf Area Index or LAI is the ratio of total upper leaf surface of vegetation dividedby the surface area of the land on which the vegetation grows. The LAI is adimensionless value, typically ranging from 0 for bare ground to 6 for a dense forest.Contents • 1 LAI in silviculture • 2 Interpretation and application of the LAI • 3 Determining LAI o 3.1 Direct method o 3.2 Indirect method o 3.3 Disadvantages of methods • 4 See also • 5 ReferencesLAI in silvicultureForestry scientists define Leaf Area Index as the one-sided green leaf area per unitground surface area in broadleaf canopies. In conifers, three different definitions havebeen used: • Total needle surface area per unit ground area • Half of the total needle surface area per unit ground area • Projected needle area per unit ground area[1]Plant anatomy, From Wikipedia, the free encyclopedia 101
  • 102. Interpretation and application of the LAIThe LAI is used to predict the photosynthetical primary production and as a referencetool for crop growth. As such, LAI plays an essential role in theoretical productionecology. An inverse exponential relation between LAI and light interception, which islinearly proportional to the primary production rate has been established:[citation needed]where Pmax designates the maximum primary production and c designates a crop-specificgrowth coefficient. This inverse exponential function is called the primary productionfunction.Determining LAIThe LAI is determined directly by taking a statistically significant sample of plants froma crop, measuring the mean leaf area per plant and dividing it by the mean available landsurface per plant. The indirect method measures light extinction and relates it to LAI.Direct methodThe mean leaf area per plant is measured by hand or by using a leaf area index meter.Traditional leaf area index meters require each plant leaf to be stripped and fed throughthe entrance of the machine, which can be likened to a kind of crude image scanner. Thisrequires stripping of the foliage of the plants and is only admissible in large-scaleexperiments.Indirect methodNewer types of LAI meters, such as the LAI-2000 [2] from LI-COR Biosciences,measure LAI in a non-destructive way by means of measuring the difference betweenlight levels on top of the crop and at ground level and using the inverse exponentialrelation given by the primary production function between light absorption and LAI.Indirect methods, in which leaf area is inferred from observations of another variable,like leaf length and width,[1] are generally faster, amendable to automation, and therebyallow for a larger number of spatial samples to be obtained. For reasons of conveniencewhen compared to the direct methods, they are becoming more and more important.Indirect methods of estimating LAI in situ can be divided in two categories: (1) indirectcontact LAI measurements such as plumb lines and inclined point quadrates[citation needed];and (2) indirect non-contact measurements.Plant anatomy, From Wikipedia, the free encyclopedia 102
  • 103. Disadvantages of methodsThe disadvantage of the direct method is that it is destructive, time consuming andexpensive, especially if the study area is very large.The disadvantage of the indirect method is that it underestimates the value of LAI.[citationneeded]See also • Normalized Difference Vegetation IndexReferences • FAO: calculation of primary production • Non-Existence of an Optimum Leaf Area Index for the Production Rate of White Clover Grown Under Constant Conditions • Chen, J.M., and Black, T.A. (1992): Defining leaf area index for non-flat leaves. Agricultural and Forest Meteorology 57: 1–12. • LAI Definition of University of Giessen, Germany 1. ^ Blanco, F.F.; Folegatti, M.V. (2003). "A new method for estimating the leaf area index of cucumber and tomato plants". Horticultura Brasileira 21 (4): 666–669. doi:10.1590/S0102-05362003000400019.PhyllocladePhylloclades are flattened, photosynthetic short shoots which are modified branches thatgreatly resemble or perform the function of leaves, as in Butchers broom (Ruscusaculeatus) as well as Asparagus and Phyllanthus species.EtymologyNew Latin phyllocladium; from Greek phyllo, leaf + klados, branch.VernationThis Australian tree fern is producing a new frond by the process of circinate vernationPlant anatomy, From Wikipedia, the free encyclopedia 103
  • 104. Vernation (from vernal, since that is when leaves "spring forth" in Temperate regions) isthe formation of new leaves or fronds. In plant anatomy, it is the arrangement of leaves ina bud.In pine trees, new leaves are short and encased in sheaths. Each leaf bundle consists of 2to 5 needles. All the leaves on one section of branch grow in length together. In thecabbage, new leaves are folded over, each covered by the previous leaf.Circinate vernationCircinate vernation is the name given to the manner in which new fern fronds emerge.As a new fern frond is formed, it is tightly curled so that the tender growing tip of thefrond (and each subdivision of the frond) is protected within a coil. At this stage it iscalled a crozier (after the shepherds crook) or fiddlehead (after the scrollwork at the topof a violin). As the lower parts of the frond expand and toughen up, they begin tophotosynthesize, supporting the further growth and expansion of the frond. In the case ofmany fronds, such as that of the Australian tree fern in the picture at right, long hairs orscales provide additional protection to the growing tips before they are fully uncoiled.Circinate vernation may also be observed in the extension of pinnae, or leaflets, in thecompound leaves of the Cycads (Division Cycadophyta).Plant evolutionary developmental biology is placed earlier . . .Section B. General Characters and Character States:I. Position and Arrangement[A. Location or Environmental Position] [B. Position] [C. Arrangement] [D. Orientation] [E. TransversePosture] [F. Longitudinal Posture] [G. General Structural Position] [H. Embryonic Position]A. Location or Environmental Position(Classification based on position of organs or parts in theirsurrounding environment)1. GeneralAerial or Epigeous. Above the ground or water; in the air.Emergent. With part(s) of plant aerial and part(s) submersed; rising out of the waterabove the surface.Epipetric. Upon rock.Epiphytic. Upon another plant.Floating. Upon the surface of the water.Submersed. Beneath the surface of the water.Subterranean or Hypogeous. Below the surface of the ground.Surficial or Epigeous. Upon or spread over the surface of the ground.2. Special(Selected location terms. See habitat prefixes in Chapter 15 and wordstems for plant organs and parts in Chapter 4 for meanings of otherlocation terms.)Aerocaulous. With aerial stems.Aerophyllous. With aerial leaves.Plant anatomy, From Wikipedia, the free encyclopedia 104
  • 105. Amphicarpous. With fruits in two environments; e.g., aerial and subterranean.Emersifolious. With emergent leaves.Epirhizous. With roots upon another plant.Flotophyllous. With floating leaves.Geoflorous. With subterranean flowers.Petrorhizous. With roots on rock.Submersicaulous. With submersed stems.Surcarpous. With fruits on surface of ground.B. Position(Classification based on location of parts or organs with respect toother dissimilar parts, or organs)1. GeneralApical or Terminal. At the top, tip, or end of a structure.Basal or Radical. At the bottom or base of a structure.Continuous. Basal, lateral, and terminal.Discontinuous. Basal and lateral, basal and terminal, or lateral and terminal; notcontinuous.Lateral or Axillary. On the side of a structure or at the nodes of the axis.2. Special(Classification based on positional terms usually applicable to individualparts)a. Androecial Position(See Perianth and Stamen Position, h. and k.)b. Branch PositionAcrocaulous. With terminal branches.Basicaulous. With basal branches.Caulous. With branches more or less evenly spaced along trunk.Subacrocaulous. With branches at or near tip of main stem.Subbasicaulous. With branches at or near base of main stem.Zonocaulous. With branches intermittently spaced along main stem.c. Cotyledon Position (Figure 6-12-3)Accumbent or Pleurorhizal. Reclinate with cotyledon edges against hypocotyl.Incumbent or Notorhizal. Reclinate with sides of cotyledons against hypocotyl.d. Flower, Fruit, Inflorescence, Infructescence PositionAcrocaulous. At the tip of the stem.Amphiflorous, Amphicarpous. Flowers or fruits above and below ground, as inAmphicarpum.Axillary. In axil of leaf.Plant anatomy, From Wikipedia, the free encyclopedia 105
  • 106. Basicaulous. Near base of stem.Cauline or Caulous. On old woody stem.Epiphyllous. From a phylloclad or peculiar bract, as in Tilia.Geoflorous, Geocarpous. Flowers or fruits below ground, as in Amphicarpum.Infrafoliar. On the stem below the leaves, as in the Arecaceae.Interfoliar. On the stem between the leaves, as in the Arecaceae.Leaf-opposed. On stem opposite the base of the leaf, as in Alchemilla.Suprafoliar. On the stem above the leaves, as in the Arecaceae.Terminal. At or near tip of branch.e. Leaf PositionAcroramous. Leaves terminal, near apex of branch.Aphyllopodic. Without blade-bearing leaves at base of plant.Basiramous. Leaves on lower part of branch.Cauline or Ramous. Leaves more or less evenly distributed on stem or branch.Phyllopodic. With blade-bearing leaves at base of plant.Radical. Leaves basal, near ground, usually from caudex or rootstock.f. Ovary PositionInferior. Other floral organs attached above ovary with hypanthium adnate to ovary.Half-inferior. Other floral organs attached around ovary with hypanthium adnate tolower half of ovary.Superior. Other floral organs attached below ovary.g. Ovule Position (Figure 6-12-4)(Based on position of ovule in locule and orientation of the micropyle and raphe--adaptedfrom Epitropous, dorsal. Ovule pendulous or hanging, micropyle above, raphe dorsal(away from ventral bundle).Epitropous, ventral. Ovule pendulous or hanging, micropyle above, raphe ventral(toward ventral bundle).Heterotropous. Ovule position not fixed in ovary.Hypotropous, dorsal. Ovule erect, micropyle below, raphe dorsal (away from ventralbundle).Hypotropous, ventral. Ovule erect, micropyle below, raphe ventral (toward ventralbundle).Pleurotropous, dorsal. Ovule horizontal, micropyle toward ventral bundle, raphe above.Pleurotropous, ventral. Ovule horizontal, micropyle toward ventral bundle. raphebelow.Plant anatomy, From Wikipedia, the free encyclopedia 106
  • 107. h. Perianth and Androecium Position (Figure 11-1)(Classification based on insertion of Floral Parts--Corolla, Calyx, andAndroecium--the androperianth)Epigyny. The condition in which the sepals, petals, stamens are attached to the floraltube above the ovary with the ovary adnate to the tube or hypanthium.Epihyperigyny. The condition in which the sepals, petals, stamens are attached to thefloral tube or hypanthium surrounding the ovary; a combination perigyny and partlyinferior ovary.Epihypogyny. The condition in which the sepals, petals, stamens are attached about half-way from the base of the ovary to the partly adnate hypanthium tube; half-inferiorinsertion of parts.Epiperigyny. The condition in which the sepals, petals, stamens are attached to the floralor hypanthium cup above the ovary with the lower part of the hypanthium completelyadnate to the ovary.Hypanepigyny. The condition in which the sepals, petals, stamens are attached to theelongate floral tube or hypanthium above the inferior ovary, as in Oenothera.Hypogyny. The condition in which the sepals, petals, stamens are attached below theovary.Perigyny. The condition in which the sepals, petals, stamens are attached to the floraltube or hypanthium surrounding the ovary with the tube or hypanthium free from theovary.i. Placenta Position (Placentation) (Figure 6-11-2)Axile. With the placentae along the central axis in a compound ovary with septa.Basal. With the placenta at the base of the ovary.Plant anatomy, From Wikipedia, the free encyclopedia 107
  • 108. Free-central. With the placenta along the central axis in a compound ovary withoutsepta.Laminate. With the placenta over the inner surface of the ovary wall.Marginal or Ventral. With the placenta along the margin of the simple ovary.Parietal. With the placentae on the wall or intruding partitions of a unilocular compoundovary.Pendulous, Apical, or Suspended. With the placenta at the top of the ovary.j. Radicle PositionAntitropous. With radicle pointing away from hilum.Syntropous. With radicle pointing toward hilum.k. Stamen Position (Figure 6-7-1)Allagostemonous. Having stamens attached to petal and torus alternately.Antipetalous. Opposite the petals.Antisepalous. Opposite the sepals.Cryptantherous. With stamens included.Diplostemonous. With stamens in two whorls, outer opposite the sepals, inner oppositepetals.Epipetalous. With stamens attached to or inserted upon petals or corolla.Episepalous. With stamens attached or inserted upon sepals or calyx.Obdiplostemonous. With stamens in two whorls, outer opposite petals, inner oppositethe sepals.Phanerantherous. With stamens exserted.l. Style PositionGynobasic. At the base of an invaginated ovary.Lateral. At the side of an ovary.Subapical. At one side near apex of ovary.Terminal or Apical. At the apex of the ovary.Plant anatomy, From Wikipedia, the free encyclopedia 108
  • 109. C. Arrangement(Classification based on location of organs or parts in relation toeach other)1. General (Figure 6-16-2)Alternate. One leaf or other structure per node.Clustered, Conglomerate, Agglomerate, Crowded, Aggregate. Parts dense, usuallyirregularly overlapping each other.Continuous. Symmetry of arrangement even, not broken.Decussate. Opposite leaves at right angle to preceding pair.Distichous. Leaves 2-ranked, in one plane.Equitant. Leaves 2-ranked with overlapping bases, usually sharply folded along midrib.Fasciculate. Leaves or other structures in a cluster from a common point.Geminate or Binate. Paired; in pairs.Imbricate. Leaves or other structures overlapping.Interrupted or Discontinuous. Symmetry of arrangement broken, with uneven lengthsof internodes.Loose, Distant, or Scattered. Parts widely separated from one another, usuallyirregularly.Opposite. Two leaves or other structures per node, on opposite sides of stem or centralaxis.Polystichous. Leaves or other structures in many rows.Rosulate. Leaves in a rosette.Secund or Unilateral. Flowers or other structures on one side of axis.Tetrastichous. Leaves or other structures in four rows.Tristichous. Leaves or other structures in three rows.Whorled, Radiate, or Verticillate. Three or more leaves or other structures per node.Plant anatomy, From Wikipedia, the free encyclopedia 109
  • 110. 2. Special(Classification based on arrangement with special terms applicable toindividual plant parts)a. Stamen Arrangement (Figure 6-7-2)(See General Arrangement for additional terms)Didymous. With stamens in two equal pairs.Didynamous. With stamens in two unequal pairs.Tetradynamous. With stamens in two groups, usually four long and two short.Tridynamous. With stamens in two equal groups of three.b. Thecal Arrangement (Figure 6-7-3)(The thecae in this classification can be conjunctive or disjunctive.)Divergent. Thecae or anther cells divaricate or separated from one another at an acuteangle to the connective or filament.Oblique. Thecae or anther cells lower on one side of connective than the other.Parallel. Thecae or anther cells along side of the connective or longitudinal to each other.Transverse or Explanate. Thecae or anther cells with maximum divergence of about 90(from the connective or filament.Plant anatomy, From Wikipedia, the free encyclopedia 110
  • 111. D. Orientation(Classification based on arrangement of parts in relation to verticalangle of divergence from a central axis or point)1. GeneralAcroscopic. Facing apically.Agglomerate, Conglomerate, Crowded, or Aggregate. Dense structures with variedangles of divergence.Antrorse. Bent or directed upward.Assurgent. Directed upward or forward.Basiscopic. Facing basally.Connivent. Convergent apically without fusion.Contorted. Twisted around a central axis; twisted.Declinate. Directed or curved downward.Deflexed. Bent abruptly downward.Dextrorse. Rising helically from right to left, a characteristic of twining stems.Inflexed. Bent abruptly inward or upward.Patent. Spreading.Pendulous. Hanging loosely or freely.Reclinate. Bent down upon the axis, no angle of divergence.Reflexed. Bent or turned downward.Retrorse. Bent or directed downward.Salient, Porrect, or Projected. Pointed outward, usually said of teeth.Sinistrorse. Rising helically from left to right, a characteristic of twining stems.Twining. Twisted around a central axis.2. Special (Classification based on stated degrees of divergence)Appressed or adpressed. Pressed closely to axis upward with angle of divergence 15° orless.Ascending. Directed upward with an angle of divergence of 16-45°.Depressed. Pressed closely to axis downward with angle of divergence of 166-180°.Descending. Directed downward with an angle of divergence of 136-165°.Divergent, Patent, or Divaricate. More or less horizontally spreading with angle ofdivergence of 15° or less up or down from the horizontal.Horizontally. Spreading outward at 90° from vertical axis or plane.Inclined. Ascending at 46-75° angle of divergenceReclined. Descending at 106-135° angle of divergence.Resupinate. Inverted or twisted 180°, as in pedicels in the Orchidaceae.Plant anatomy, From Wikipedia, the free encyclopedia 111
  • 112. E. Transverse Posture (Figure 6-11-3)(Classification based on position of ends of single structure inrelation to its center or transverse axis)Applanate or Plane. Flat, without vertical curves or bends.Arcuate. Curved like a crescent, can be downward or upward.Cernuous. Drooping.Flexuous. With a series of long or open vertical curves at right angles to the central axis.Geniculate. Abruptly bent vertically, usually near the base.Incurved. Curved inward or upward.Lorate. With elongate vertical waves in the margins or sides at right angles to thelongitudinal axis.Recurved. Curved outward or downward.Squarrose. Usually sharply curved downward or outward in the apical region, as thebracts of some species of Aster.Undulate. With a series of vertical curves at right angles to the central axis.Plant anatomy, From Wikipedia, the free encyclopedia 112
  • 113. F. Longitudinal Posture (Figure 6-11-4)(Classification based on position of the sides of a single structure inrelation to its central axis)Conduplicate. Longitudinally folded upward or downward along the central axis so thatventral and/or dorsal sides face each other.Geniculate. Abruptly bent horizontally, usually in series.Induplicate. Having margins bent inward and touching margin of each adjacentstructure.Involute. Margins or outer portion of sides rolled inward over upper or ventral surface.Plicate. With a series of longitudinal folds; plaited.Revolute. Margins or outer portion of sides rolled outward or downward over lower ordorsal surface.Rolled. Sides enrolled, usually loosely, over upper or lower surfaces.Sinuate. Long horizontal curves in the body of the structure parallel to the central axis.Straight. Without a curve, bend, or angle.Tortuous. Irregularly twisted.Valvate. Sides enrolled, adaxially or abaxially so that margins touch.G. General Structural Position(Pertains to regional locations on a structure)1. GeneralAbaxial. Away from the axis; the lower surface of the leaf; dorsal.Adaxial. Next to the axis; facing the stem; ventral.Apical. At or near the tip.Basal. At or near the bottom.Central. In the middle or middle plane of a structure.Circumferential. At or near the circumference; surrounding a rounded structure.Plant anatomy, From Wikipedia, the free encyclopedia 113
  • 114. Distal. Away from the point of origin or attachment.Dorsal. Pertaining to the surface most distant from the axis; back of an outer face oforgan; lower side of leaf; abaxial.Marginal. Pertaining to the border or edge.Medial. Upon or along the longitudinal axis.Peripheral. On the outer surface or edge.Proximal. Near the point of origin or attachment.Subbasal. Near the base.Subterminal. Near the apex.Ventral. Pertaining to the surface nearest the axis; inner face of an organ; the uppersurface of the leaf; adaxial.2. Special(Selected terms for location on a structure. The meanings of manyadditional terms can be determined from the positional prefixes andword stems of plant organs and parts in Chapter 4.)Acrocaulous. At tip of stem.Basipetiolar. At the base of the petiole.Centroramous. At the center of the branch.Dorsilaminar. On dorsal side of blade.Laterospermous. On the side of the seed.Pericarpous. Around the fruit.Suprarhizous. On top of the root.Ventristipular. On ventral side of stipule.H. Embryonic Position(Classification based on position and arrangement of immatureorgans or parts)1. Aestivation or Prefloration (Figure 6-12-1)(Classification based on position of embryonic perianth parts. Calyxand corolla may have different aestivation types.)Alternate. Having structure in two rows or series so that the inner structure has itsmargins overlapped by a margin from each adjacent outer structure.Cochleate. Having one hollow or helmet-shaped structure which encloses or covers theothers.Plant anatomy, From Wikipedia, the free encyclopedia 114
  • 115. Contorted. Having several struc tures in a whorl or close spiral with one margincovering the margin of an adjacent structure.Convolute. Having one leaf or perianth part rolled in another, usually twisted apically.Imbricate. Having margins overlapping.Induplicate. Having margins bent inward and touching margin of adjacent structure.Quincuncial. Having five structures, two of which are exterior, two interior, and a fifthwith one margin covering interior structure and other margin covered by that of one ofthe exterior structures.Valvate. Having margins of adjacent structures touching at edges only.Vexillate. Having one structure larger than others which is folded over smaller enclosedstructures. 2. Cotyledon Ptyxis (Figure 6-12-2) (Classification based on position of cotyledons in seed)Conduplicate. Cotyledons folded lengthwise along midrib with one cotyledon coveringother and inner cotyledon covering hypocotyl.Contortuplicate. With weirdly folded corrugate cotyledons.Diplecolobal. With incumbent cotyledons folded two or more times.Spirolobal. With incumbent cotyledons folded once.3. Ptyxis (Figure 6-12-2)(Classification based on rolling or folding of individual embryonicleaves and arrangement of embryonic leaves within a structure;Plant anatomy, From Wikipedia, the free encyclopedia 115
  • 116. vernation according to most authors). Adapted from Davis andHeywood (1963).Circinate. With lamina rolled from apex to base with apex in center of coil.Conduplicate. With lamina folded once adaxially along midrib or midvein.Convolute. With one lamina enrolled in another lamina.Corrugate. With lamina irregularly folded in all directions, wrinkled.Curvative or arcuate. With lamina folded transversely into an arc.Implicate. With both lamina margins folded sharply inward.Inclinate. With lamina folded or curved transversely near the apex.Involute. With lamina margins enrolled adaxially.Planate or Plain. With lamina flat, without folds or rolls.Plicate. With many longitudinal folds in lamina.Reclinate. With lamina folded or curved backwards from near its base so that embryonicblade is parallel to its petiole, hypocotyl, or stem.Replicate. With lamina folded once abaxially along midrib or midvein.Revolute. With lamina margins enrolled abaxially.Supervolute. With lamina with one edge tightly enrolled and with the other looselyenrolled covering the first, loosely convolute.Plant stem Stem showing internode and nodes plus leaf petiole and new stem rising from node. A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence (flowers), cones or other stems etc. The internodes act as spaces that distance one node from another. The term shoots is often confused with stems; shoots generally refer to new fresh plant growth and does include stems but also to other structures like leaves or flowers. The other main structural axis of plants is the root. In most plants stems are located above the soil surface but some plants have underground stems.Plant anatomy, From Wikipedia, the free encyclopedia 116
  • 117. Stems have four main functions which are:[1] • Support for and the elevation of leaves, flowers and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits. • Transport of fluids between the roots and the shoots in the xylem and phloem. • Storage of nutrients. • The production of new living tissue. The normal life span of plant cells is one to three years. Stems have cells called meristems that annually generate new living tissue.Contents • 1 Specialized terms for stems • 2 Stem structure o 2.1 Dicot stems o 2.2 Monocot stems o 2.3 Gymnosperm stems o 2.4 Fern stems • 3 Economic importance • 4 ReferencesSpecialized terms for stems Stem showing internode and nodes plus leaf petioles. Stems are often specialized for storage, asexual reproduction, protection or photosynthesis, including the following: • Acaulescent - plants with very short stems that appear to have no stems. The leaves appear to rise out of the ground, e.g. some Viola. • Arborescent - tree like with woody stems normally with a single trunk. • Bud - an embryonic shoot with immature stem tip. • Bulb - a short vertical underground stem with fleshy storage leaves attached, e.g. onion, daffodil, tulip. Bulbs often function in reproduction by splitting to form new bulbs or producing small new bulbs termed bulblets. Bulbs are a combination of stem and leaves so may better be considered as leaves because the leaves make up the greater part. • Caespitose - when stems grow in a tangled mass or clump or in low growing mats. • Cladophyll - a flattened stem that appears leaf like and is specialized for photosynthesis, e.g. asparagus, cactus pads. • Climbing - stems that cling or wrap around other plants or structures. • Corm - a short enlarged underground, storage stem, e.g. taro, crocus, gladiolus. • Decumbent - stems that lay flat on the ground and turn upwards at the ends.Plant anatomy, From Wikipedia, the free encyclopedia 117
  • 118. • Fruticose - stems that grow shrub like with woody like habit. • Herbaceous - non woody, they die at the end of the growing season. • Pseudostem - A false stem made of the rolled bases of leaves, which may be 2 or 3 m tall as in banana • Rhizome - a horizontal underground stem that functions mainly in reproduction but also in storage, e.g. most ferns, iris • Runner (plant part) - a type of stolon, horizontally growing on top of the ground and rooting at the nodes. e.g. strawberry, spider plant. • Scape - a stem that holds flowers that comes out of the ground and has no normal leaves. Hosta, Lily, Iris. • Stolons - a horizontal stem that produces rooted plantlets at its nodes and ends, forming near the surface of the ground. • Tree - a woody stem that is longer than 5 meters with a main trunk. • Thorns - a reduced stem with a sharp point and rounded shape. e.g. honey locust, hawthorn. • Tuber - a swollen, underground storage stem adapted for storage and reproduction, e.g. potato. • Woody - hard textured stems with secondary xylem.Stem structure Flax stem cross-section, showing locations of underlying tissues. Ep = epidermis; C = cortex; BF = bast fibres; P = phloem; X = xylem; Pi = pith See also: Stele (biology) Stem usually consist of three tissues, dermal tissue, ground tissue and vascular tissue. The dermal tissue covers the outer surface of the stem and usually functions to waterproof, protect and control gas exchange. The ground tissueusually consists mainly of parenchyma cells and fills in around the vascular tissue. Itsometimes functions in photosynthesis. Vascular tissue provides long distance transportand structural support. Most or all ground tissue may be lost in woody stems. The dermaltissue of aquatic plants stems may lack the waterproofing found in aerial stems. Thearrangement of the vascular tissues varies widely among plant species.Dicot stemsDicot stems with primary growth have pith in the center, with vascular bundles forming adistinct ring visible when the stem is viewed in cross section. The outside of the stem iscovered with an epidermis, which is covered by a waterproof cuticle. The epidermis alsomay contain stomata for gas exchange and hairs. A cortex of parenchyma cells liesbetween the epidermis and vascular bundles.Woody dicots and many nonwoody dicots have secondary growth originating from theirlateral or secondary meristems: the vascular cambium and the cork cambium orphellogen. The vascular cambium forms between the xylem and phloem in the vascularPlant anatomy, From Wikipedia, the free encyclopedia 118
  • 119. bundles and connects to form a continuous cylinder. The vascular cambium cells divideto produce secondary xylem to the inside and secondary phloem to the outside. As thestem increases in diameter due to production of secondary xylem and secondary phloem,the cortex and epidermis are eventually destroyed. Before the cortex is destroyed, a corkcambium develops there. The cork cambium divides to produce waterproof cork cellsexternally and sometimes phelloderm cells internally. Those three tissues form theperiderm, which replaces the epidermis in function. Areas of loosely-packed cells in theperiderm that function in gas exchange are called lenticels.Secondary xylem is commercially important as wood. The seasonal variation in growthfrom the vascular cambium is what creates yearly tree rings in temperate climates. Treerings are the basis of dendrochronology, which dates wooden objects and associatedartifacts. Dendroclimatology is the use of tree rings as a record of past climates. Theaerial stem of an adult tree is called a trunk. The dead, usually darker inner wood of alarge diameter trunk is termed the heartwood. The outer, living wood is termed thesapwood.Monocot stems The trunk of this redwood tree is its stem. Vascular bundles are present throughout the monocot stem, although concentrated towards the outside. This differs from the dicot stem that has a ring of vascular bundles and often none in the center. The shoot apex in monocot stems is more elongated. Leaf sheathes grow up around it, protecting it. This is true to some extent ofalmost all monocots. Monocots rarely produce secondary growth and are thereforeseldom woody. However, many monocot stems increase in diameter via anamoloussecondary growth.Gymnosperm stemsAll gymnosperms are woody plants. Their stems are similar in structure to woody dicotsexcept that most gymnosperms produce only tracheids in their xylem, not the vesselsfound in dicots. Gymnosperm wood also often contains resin ducts. Woody dicots arecalled hardwoods, e.g. oak, maple and walnut. In contrast, softwoods are gymnosperms, such as pine, spruce and fir. Tasmanian tree fern Fern stems Most ferns have rhizomes with no vertical stem. The exception is tree ferns, with vertical stems up to about 20 meters. The stem anatomy of ferns is more complicated than that of dicots because fern stems often have one or more leafgaps in cross section. A leaf gap is where the vascular tissue branches off to a frond. Incross section, the vascular tissue does not form a complete cylinder where a leaf gapPlant anatomy, From Wikipedia, the free encyclopedia 119
  • 120. occurs. Fern stems may have solenosteles or dictyosteles or variations of them. Manyfern stems have phloem tissue on both sides of the xylem in cross-section.Economic importance White and green asparagus - crispy stems are the edible parts of this vegetable There are thousands of species whose stems have economic uses. Stems provide a few major staple crops such as potato and taro. Sugar cane stems are a major source of sugar. Maple sugar is obtained from trunks of maple trees. Vegetables from stems are asparagus, bamboo shoots, cactus pads or nopalitos, kohlrabi, and water chestnut. The spice, cinnamon is bark from a tree trunk. Cellulose from tree trunks is a food additive in bread, grated Parmesan cheese, and other processed foods. Gum arabic is animportant food additive obtained from the trunks of Acacia senegal trees. Chicle, themain ingredient in chewing gum, is obtained from trunks of the chicle tree.Medicines obtained from stems include quinine from the bark of cinchona trees, camphordistilled from wood of a tree in the same genus that provides cinnamon, and the musclerelaxant curare from the bark of tropical vines.Wood is a used in thousands of ways, e.g. buildings, furniture, boats, airplanes, wagons,car parts, musical instruments, sports equipment, railroad ties, utility poles, fence posts,pilings, toothpicks, matches, plywood, coffins, shingles, barrel staves, toys, tool handles,picture frames, veneer, charcoal and firewood. Wood pulp is widely used to make paper,cardboard, cellulose sponges, cellophane and some important plastics and textiles, suchas cellulose acetate and rayon. Bamboo stems also have hundreds of uses, includingpaper, buildings, furniture, boats, musical instruments, fishing poles, water pipes, plantstakes, and scaffolding. Trunks of palm trees and tree ferns are often used for building.Reed stems are also important building materials in some areas.Tannins used for tanning leather are obtained from the wood of certain trees, such asquebracho. Cork is obtained from the bark of the cork oak. Rubber is obtained from thetrunks of Hevea brasiliensis. Rattan, used for furniture and baskets, is made from thestems of tropical vining palms. Bast fibers for textiles and rope are obtained from stemsinclude flax, hemp, jute and ramie. The earliest paper was obtained from the stems ofpapyrus by the ancient Egyptians.Amber is fossilized sap from tree trunks; it is used for jewelry and may contain ancientanimals. Resins from conifer wood are used to produce turpentine and rosin. Tree bark isoften used as a mulch and in growing media for container plants.Some ornamental plants are grown mainly for their attractive stems, e.g.: • White bark of paper birch • Twisted branches of corkscrew willow and Harry Lauders walking stick (Corylus avellana Contorta) • Red, peeling bark of paperbark maplePlant anatomy, From Wikipedia, the free encyclopedia 120
  • 121. References 1. ^ Raven, Peter H., Ray Franklin Evert, and Helena Curtis. 1981. Biology of plants. New York, N.Y.: Worth Publishers.ISBN 0-87901-132-7OvuleThis article is about the plant structure. For animal ovules, see ovum . Location of ovules inside a Helleborus foetidus flower Ovule literally means "small egg." In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: The integuments forming its outer layer, the nucellus (or megasporangium), and the megaspore-derived female gametophyte (or megagametophyte) in its center. The megagametophyte (also called embryo sac in flowering plants) produces the egg cell for fertilization. Afterfertilization, the ovule develops into a seed.Contents • 1 Location within the plant • 2 Ovule parts and development o 2.1 Integuments, micropyle and chalaza o 2.2 Nucellus, megaspore and perisperm o 2.3 Megagametophyte and embryo sac o 2.4 Zygote, embryo and endosperm • 3 References • 4 See alsoLocation within the plantIn flowering plants, the ovule is located within the actual flower, the part of the carpelknown as the ovary, which ultimately becomes the fruit. Depending on the plant, flowersmay have one or multiple ovules per ovary. The ovule is attached to the placental wall ofthe ovary through a structure known as the funiculus, the plant equivalent of an umbilicalcord. Different patterns of ovule attachment, or placentation, can be found among plants:In parietal placentation, the ovules are attached to the outer ovary wall, whereas in freecentral placentation, they are attached to a central column within the ovary. In axileplacentation, they are attached to radial spokes within the ovary.In gymnosperms such as conifers and similar plants, the ovules are borne unenclosed onthe surface of an ovuliferous (ovule-bearing) scale, usually within an ovulate cone (alsocalled megastrobilus).Plant anatomy, From Wikipedia, the free encyclopedia 121
  • 122. Ovule parts and developmentPlant ovules: Gymnosperm ovule on left, angiosperm ovule (inside ovary) on rightThe ovule is composed of diploid maternal tissue that gives rise to the haploid tissue ofthe female gametophyte. The maternal tissues of the ovule include the integuments andthe nucellus. The next "generation" formed within the ovule are the haploid megasporeand megagametophyte, or embryo sac. After fertilization of the egg cell and formation ofa zygote, the ovule contains the embryo of the next sporophyte generation and, inflowering plants, the triploid endosperm.Integuments, micropyle and chalazaThe integuments are the outer cell layers of the ovule enclosing the nucellus.Gymnosperms typically have one integument layer while angiosperms typically havetwo. The integuments develop into the seed coat when the ovule matures afterfertilization.The integuments do not enclose the nucellus completely but leave an opening at its apexreferred to as the micropyle. The micropyle opening allows the pollen tube to enter theovule for fertilization. In gymnosperms (e.g. conifers), the pollen itself is drawn into theovule and the micropyle opening closes after pollination. During germination, theseedlings radicle emerges through the micropyle.Located opposite from the micropyle is the chalaza where the nucellus is joined to theinteguments. Nutrients from the plant travel through the phloem of the vascular system tothe funiculus and outer integument and from there apoplastically and symplasticallythrough the chalaza to the nucellus inside the ovule. In chalazogamous plants, the pollentubes enter the ovule through the chalaza instead of the micropyle opening.Nucellus, megaspore and perispermThe nucellus (plural: nucelli) is the central portion of the ovule inside the integuments. Itconsists of diploid maternal tissue and has the function of a megasporangium. Inimmature ovules, it contains a megasporocyte (megaspore mother cell), which undergoessporogenesis via meiosis. Three of the four haploid cells produced in meiosis degenerate,leaving one surviving megaspore inside the nucellus. After fertilization, the nucellusdevelops into the perisperm that feeds the embryo. In some plants, the diploid tissue ofthe nucellus can give rise to a seed through a mechanism of asexual reproduction callednucellar embryony.Plant anatomy, From Wikipedia, the free encyclopedia 122
  • 123. Megagametophyte and embryo sac Ovule with embryo sac: egg cell (yellow), synergids (orange), central cell with two polar nuclei (bright green), and antipodals (dark green) The haploid megaspore inside the nucellus gives rise to the female gametophyte (megagametophyte). In gymnosperms, the female gametophyte consists of around 2000 nuclei and forms archegonia which produce the egg cells for fertilization. In flowering plants, the megagametophyte, also referred to as embryo sac, is much smaller and typically consists of only seven cells and eight nuclei. The embryo sac develops from the megaspore throughthree rounds of mitotic divisions. The cell closest to the micropyle opening of theinteguments differentiates into the egg cell, with two synergid cells by its side that maybe involved in the production of signals that guide the pollen tube. Three antipodal cellsform on the opposite (chalazal) end of ovule and later degenerate, serving no obviousfunction. The large central cell of the embryo sac contains two polar nuclei.Zygote, embryo and endospermThe pollen tube releases two sperm nuclei into the ovule. In gymnosperms, fertilizationoccurs within the archegonia produced by the female gametophyte. While it is possiblethat several egg cells are present and fertilized, typically only one zygote will developinto a mature embryo as the resources within the seed are limited.In flowering plants, one sperm nucleus fuses with the egg cell into a zygote, the otherfuses with the two polar nuclei of the central cell to give rise to the triploid endosperm.This double fertilization is unique to flowering plants. The plant stores nutrients such asstarch, proteins and oils in the endosperm as a food source for the developing embryo andseedling, serving a similar function to the yolk of animal eggs. The endosperm is alsocalled the albumen of the seed.References • P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): Biology of Plants, 7th Edition, W.H. Freeman and Company Publishers, New York, ISBN 0-7167-1007-2See also • Carpel (Gynoecium) • Ovum • Alternation of generationsPlant anatomy, From Wikipedia, the free encyclopedia 123
  • 124. Gynoecium (placed already)Alternation of generationsSporic or diplohaplontic life cycle. A diploid (2n) sporophyte undergoes meiosis toproduce haploid (1n) reproductive cells, often called spores. Haploid cells undergomitosis to produce a gametophyte. The gametophyte produces haploid gametes whichfuse to form a diploid zygotic sporophyte.The Alternation of phases (or generations)[1] describes the life cycle of plants, fungiand protists. A multicellular diploid phase alternates with a multicellular haploid phase.The term can be confusing for people familiar only with the life cycle of a typical animal.A more understandable name would be "alternation of phases of a single generation"because we usually consider a generation of a species to encompass one complete lifecycle. The life cycle of organisms with "alternation of generations" is characterized byeach phase consisting of one of two distinct organisms: a gametophyte (thallus (tissue) orplant), which is genetically haploid, and a sporophyte (thallus or plant), which isgenetically diploid. A haploid plant of the gametophyte generation produces gametes bymitosis. Two gametes (originating from different organisms of the same species or fromthe same organism) combine to produce a zygote, which develops into a diploid plant ofthe sporophyte generation. This sporophyte produces spores by meiosis, which germinateand develop into a gametophyte of the next generation. This cycle, from gametophyte togametophyte, is the way in which all land plants and many algae undergo sexualreproduction.Plant anatomy, From Wikipedia, the free encyclopedia 124
  • 125. Contents • 1 Distinctions • 2 Fungi • 3 Protists • 4 Plants o 4.1 Non-vascular plants o 4.2 Vascular plants • 5 See also • 6 ReferencesDistinctionsIt is often stated that the distinction of "free-living" is important, because all sexuallyreproducing organisms can be thought to involve alternating phases, at least at thecellular level as meiosis. However, alternation of generations implies that both the diploidand haploid stages are multicellular and this is more important than "free-living".[2] Sucha distinction changes the concept to one separating animals and plants. The gametophyteand sporophyte are usually separate, independent organisms in basal algae such as Ulvalactuca, where the gametes are free-swimming, and the zygote is formed in the water. Bycontrast, in land plants the sporophytes are to a greater or lesser extent dependent on thegametophytes, and vice-versa, especially in the gymnosperms and angiosperms. Indeed itis a defining characteristic of the land plants, or embryophytes (and hence the name), thata developing multicellular sporophyte is, for at least the first stages of its development,nurtured by the gametophyte, as can be seen most clearly in the bryophytes.All plants have diploid sporophyte and haploid gametophyte stages that are multicellular,and the differences between plant groups are in the relative sizes, forms, and trophicabilities of the gametophyte or sporophyte forms, as well as the level of differentiation inthe gametophytes. An example would be comparing pollen and ovules to bisexualgametophyte thalli. Both approaches are discussed in this article.Life cycles in which there is no multicellular diploid phase are referred to as haplontic.Life cycles with alternating haploid and diploid phases are diplohaplontic, but theequivalent terms diplobiontic, haplodiplontic, or dibiontic are also in use. Two maintypes of diplohaplontic (alternating) life-cycles are recognized: if the sporophyte and thegametophyte generations are more or less identical in form, the life cycle is said to beisomorphic, meaning "same form". If the generations have very different morphology,the life cycle is called heteromorphic meaning "different forms".Heterogamy is a term used to describe alternation between parthenogenic and sexuallyreproductive phases that occurs in some animals. Although conceptually similar to"alternation of generations", the genetics of heterogamy is significantly different.FungiFungal mycelia are typically haploid. When mycelia of different mating types meet, theyproduce two multinucleate ball-shaped cells, which join via a "mating bridge". Nucleimove from one mycelium into the other, forming a heterokaryon (meaning "differentnuclei"). This process is called plasmogamy. Actual fusion to form diploid nuclei iscalled karyogamy, and may not occur until sporangia are formed. Karogamy produces adiploid zygote, which is a short-lived sporophyte that soon undergoes meiosis to formhaploid spores. When the spores germinate, they develop into new mycelia.Plant anatomy, From Wikipedia, the free encyclopedia 125
  • 126. ProtistsSome protists undergo an alternation of generations, including the slime molds,foraminifera, and many marine algae.The life cycle of slime molds is very similar to that of fungi. Haploid spores germinate toform swarm cells or myxamoebae. These fuse in a process referred to as plasmogamy andkaryogamy to form a diploid zygote. The zygote develops into a plasmodium, and themature plasmodium produces, depending on the species, one to many fruiting bodiescontaining haploid spores.Foraminifera undergo a heteromorphic alternation of generations between a haploidgamont and a diploid agamont phases. The single-celled haploid organism is typicallymuch larger than the diploid organism.Alternation of generations occurs in almost all marine algae. In most red algae, manygreen algae, and a few brown algae, the phases are isomorphic and free-living. Somespecies of red algae have a complex triphasic alternation of generations. Kelp are anexample of a brown alga with a heteromorphic alternation of generations. Species fromthe genus Laminaria have a large sporophytic thallus that produces haploid spores whichgerminate to produce free-living microscopic male and female gametophytes.PlantsNon-vascular plantsBryophyte plants including the liverworts, hornworts and mosses undergo an alternationof generations; the gametophyte generation is the most common. The haploidgametophyte produces haploid gametes in multicellular gametangia. Female gametangiaare called archegonium and produce eggs, while male structures called antheridiumproduce sperm. Water is required so that the sperm can swim to the archegonium, wherethe eggs are fertilized to form the diploid zygote. The zygote develops into a sporophytethat is dependent on the parent gametophyte. Mature sporophytes produce haploid sporesby meiosis in sporangia. When a spore germinates, it grows into another gametophyte.They are also seedless.Diagram of alternation ofA liverwort gametophyte A liverwort sporophyte.generations in liverworts.[edit] Vascular plantsFerns and their allies, including clubmoss and horsetails, reproduce via an alternation ofgenerations. The conspicuous plant observed in the field is the diploid sporophyte. Thisplant creates by meiosis single-celled haploid spores which are shed and dispersed by thewind (or in some cases, by floating on water). If conditions are right, a spore willgerminate and grow into a rather inconspicuous plant body called a prothallus. Thehaploid prothallus does not resemble the sporophyte, and as such ferns and their allieshave a heteromorphic alternation of generations. The prothallus is short-lived, but carriesPlant anatomy, From Wikipedia, the free encyclopedia 126
  • 127. out sexual reproduction, producing the diploid zygote that then grows out of theprothallus as the sporophyte. A gametophyteA sporophyte ofThe underside of aDiagram of(prothallus) ofDicksonia Dicksonia antarcticaalternation ofDicksonia sp. antarctica. frond showing the sori,generations in ferns. or spore-producing structures.In seed plants, the sporophyte is the dominant multicellular phase, and the gametophytesare both strongly reduced in size and different in morphology. Female gametophytesoccur only in the seeds, and male gametophytes only in the pollen. A gymnosperm seed,growing on the diploid sporophyte parent, initially contains a haploid femalegametophyte bearing a haploid egg cell enclosed in a cup-shaped structure known as thearchegonium. The egg is fertilised by a sperm nucleus from a pollen grain, that contains aminiature male gametophyte. The resulting diploid zygote develops into the seed embryo,which is the diploid sporophyte of the next generation. During its development, which ingymnosperms may take 2-3 years, the offspring sporophyte and its parent gametophyteare both nurtured by the grandparent sporophyte until the seed is ripe enough to bereleased.See also • Evolutionary history of plants#phases: Evolutionary origin of the alternation of phasesReferences 1. ^ Stewart, W.N. and Rothwell, G.W. 1993. Paleobotany and the evolution of plants, Second edition. Cambridge University Press, Cambridge, UK. ISBN 0- 521-38294-7 2. ^ Taylor, T.N.; et al. (2005). "Life history biology of early land plants: Understanding the gametophyte phase". Proceedings of the National Academy of Sciences 102: 5892–5897. doi:10.1073/pnas.0501985102. PMID 15809414.Plant anatomy, From Wikipedia, the free encyclopedia 127
  • 128. SeedFor other uses, see Seed (disambiguation).Contents • 1 Seed structure • 2 Seed production o 2.1 Kinds of seeds o 2.2 Seed development o 2.3 Seed size and seed set • 3 Seed functions o 3.1 Embryo nourishment o 3.2 Seed dispersal 3.2.1 By wind (anemochory) 3.2.2 By water (hydrochory) 3.2.3 By animals (zoochory) o 3.3 Seed dormancy and protection • 4 Seed germination o 4.1 Inducing germination • 5 Origin and evolution • 6 Economic importance o 6.1 Edible seeds o 6.2 Poison and food safety o 6.3 Other uses • 7 Trivia • 8 See also • 9 References • 10 External links A ripe red jalapeño cut open to show the seeds A seed / si d/ (help·info) (in some plants, referred to as a kernel) is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant. The formation of the seed completes the process of reproduction in seed plants (started with the development of flowers and pollination), with the embryo developed from the zygote and the seed coat from the integuments of the ovule. Seeds have been an important development in the reproduction and spread of flowering plants, relative to more primitive plants like mosses, ferns and liverworts,which do not have seeds and use other means to propagate themselves. This can be seenby the success of seed plants (both gymnosperms and angiosperms) in dominatingbiological niches on land, from forests to grasslands both in hot and cold climates.The term seed also has a general meaning that predates the above — anything that can besown i.e. "seed" potatoes, "seeds" of corn or sunflower "seeds". In the case of sunflowerPlant anatomy, From Wikipedia, the free encyclopedia 128
  • 129. and corn "seeds", what is sown is the seed enclosed in a shell or hull, and the potato is atuber.Seed structureThe parts of an avocado seed (a dicot), showing the seed coat, endosperm, and embryo.A typical seed includes three basic parts: (1) an embryo, (2) a supply of nutrients for theembryo, and (3) a seed coat.The embryo is an immature plant from which a new plant will grow under properconditions. The embryo has one cotyledon or seed leaf in monocotyledons, twocotyledons in almost all dicotyledons and two or more in gymnosperms. The radicle isthe embryonic root. The plumule is the embryonic shoot. The embryonic stem above thepoint of attachment of the cotyledon(s) is the epicotyl. The embryonic stem below thepoint of attachment is the hypocotyl.Within the seed, there usually is a store of nutrients for the seedling that will grow fromthe embryo. The form of the stored nutrition varies depending on the kind of plant. Inangiosperms, the stored food begins as a tissue called the endosperm, which is derivedfrom the parent plant via double fertilization. The usually triploid endosperm is rich in oilor starch and protein. In gymnosperms, such as conifers, the food storage tissue is part ofthe female gametophyte, a haploid tissue. In some species, the embryo is embedded in theendosperm or female gametophyte, which the seedling will use upon germination. Inothers, the endosperm is absorbed by the embryo as the latter grows within thedeveloping seed, and the cotyledons of the embryo become filled with this stored food.At maturity, seeds of these species have no endosperm and are termed exalbuminousseeds. Some exalbuminous seeds are bean, pea, oak, walnut, squash, sunflower, andradish. Seeds with an endosperm at maturity are termed albuminous seeds. Mostmonocots (e.g. grasses and palms) and many dicots (e.g. brazil nut and castor bean) havealbuminous seeds. All gymnosperm seeds are albuminous.The seed coat (or testa) develops from the tissue, the integument, originally surroundingthe ovule. The seed coat in the mature seed can be a paper-thin layer (e.g. peanut) orsomething more substantial (e.g. thick and hard in honey locust and coconut). The seedcoat helps protect the embryo from mechanical injury and from drying out.In addition to the three basic seed parts, some seeds have an appendage on the seed coatsuch an aril (as in yew and nutmeg) or an elaiosome (as in Corydalis) or hairs (as inPlant anatomy, From Wikipedia, the free encyclopedia 129
  • 130. cotton). There may also be a scar on the seed coat, called the hilum; it is where the seedwas attached to the ovary wall by the funiculus.Seed productionImmature Elm seeds.Seeds are produced in several related groups of plants, and their manner of productiondistinguishes the angiosperms ("enclosed seeds") from the gymnosperms ("naked seeds").Angiosperm seeds are produced in a hard or fleshy structure called a fruit that enclosesthe seeds, hence the name. (Some fruits have layers of both hard and fleshy material). Ingymnosperms, no special structure develops to enclose the seeds, which begin theirdevelopment "naked" on the bracts of cones. However, the seeds do become covered bythe cone scales as they develop in some species of conifer.Kinds of seedsThere are a number of modifications to seeds by different groups of plants. One exampleis that of the so-called stone fruits (such as the peach), where a hardened fruit layer ( theendocarp) surrounds the actual seed and is fused to it.Many structures commonly referred to as "seeds" are actually dry fruits. Sunflower seedsare sold commercially while still enclosed within the hard wall of the fruit, which must besplit open to reach the seed.Seed developmentThe inside of a Ginkgo seed, showing a well-developed embryo, nutritive tissue(megagametophyte), and a bit of the surrounding seed coat.Plant anatomy, From Wikipedia, the free encyclopedia 130
  • 131. Diagram of the internal structure of a dicot seed and embryo. (a) seed coat, (b)endosperm, (c) cotyledon, (d) hypocotyl.The seed, which is an embryo with two points of growth (one of which forms the stemsthe other the roots) is enclosed in a seed coat with some food reserves. Angiosperm seedsconsist of three genetically distinct constituents: (1) the embryo formed from the zygote,(2) the endosperm, which is normally triploid, (3) the seed coat from tissue derived fromthe maternal tissue of the ovule. In angiosperms, the process of seed development beginswith double fertilization and involves the fusion of the egg and sperm nuclei into azygote. The second part of this process is the fusion of the polar nuclei with a secondsperm cell nucleus, thus forming a primary endosperm. Right after fertilization the zygoteis mostly inactive but the primary endosperm divides rapidly to form the endospermtissue. This tissue becomes the food that the young plant will consume until the rootshave developed after germination or it develops into a hard seed coat. The seed coatforms from the two integuments or outer layers of cells of the ovule, which derive fromtissue from the mother plant, the inner integument forms the tegmen and the outer formsthe testa. When the seed coat forms from only one layer it is also called the testa, thoughnot all such testa are homologous from one species to the next.In gymnosperms, the two sperm cells transferred from the pollen do not develop seed bydouble fertilization but instead only one sperm fertilizes the egg while the other is notused. The seed is composed of the embryo (the result of fertilization) and tissue from themother plant, which also form a cone around the seed in coniferous plants like Pine andSpruce.The ovules after fertilization develop into the seeds; the main parts of the ovule are thefunicle; which attaches the ovule to the placenta, the nucellus; the main region of theovule were the embryo sac develops, the micropyle; A small pore or opening in the ovulewhere the pollen tube usually enters during the process of fertilization, and the chalaza;the base of the ovule opposite the micropyle, where integument and nucellus are joinedtogether.[1]Plant anatomy, From Wikipedia, the free encyclopedia 131
  • 132. The shape of the ovules as they develop often affects the finale shape of the seeds. Plantsgenerally produce ovules of four shapes: the most common shape is called anatropous,with a curved shape. Orthotropous ovules are straight with all the parts of the ovule linedup in a long row producing an uncurved seed. Campylotropous ovules have a curvedembryo sac often giving the seed a tight “c” shape. The last ovule shape is calledamphitropous, where the ovule is partly inverted and turned back 90 degrees on its stalkor funicle.In the majority of flowering plants the zygotes first division is transversely orientated inregards to the long axis and this establishes the polarity of the embryo. The upper orchalazal pole becomes the main area of growth of the embryo, while the lower ormicropylar pole produces the stalk-like suspensor that attaches to the micropyle. Thesuspensor absorbs and manufacturers nutrients from the endosperm that are utilizedduring the embryos growth.[2]The embryo is composed of different parts; the epicotyle will grow into the shoot, theradicle grows into the primary root, the hypocotyl connects the epicotyle and the radicle,the cotyledons form the seed leaves, the testa or seed coat forms the outer covering ofthe seed. Monocotyledonous plants like corn, have other structures; instead of thehypocotyle-epicotyle, it has a coleoptile that forms the first leaf and connects to thecoleorhiza that connects to the primary root and adventitious roots form from the sides.The seeds of corn are constructed with these structures; pericarp, scutellum (single largecotyledon) that absorbs nutrients from the endosperm, endosperm, plumule, radicle,coleoptile and coleorhiza - these last two structures are sheath-like and enclose theplumule and radicle, acting as a protective covering. The testa or seed coats of bothmonocots and dicots are often marked with patterns and textured markings, or have wingsor tufts of hair.Seed size and seed setSeeds are very diverse in size. The dust-like orchid seeds are the smallest with about onemillion seeds per gram, they are often embryonic seeds with immature embryos and nosignificant energy reserves. Orchids and a few other groups of plants are myco-heterotrophs which depend on mycorrhizal fungi for nutrition during germination and theearly growth of the seedling. Some terrestrial Orchid seedlings, in fact, spend the firstfew years of their life deriving energy from the fungus and do not produce green leaves.[3]At over 20 kg, the largest seed is the coco de mer. Plants that produce smaller seeds cangenerate many more seeds per flower, while plants with larger seeds invest moreresources into those seeds and normally produce fewer seeds. Small seeds are quicker toripen and can be dispersed sooner, so fall blooming plants often have small seeds. Manyannual plants produce great quantities of smaller seeds; this helps to ensure that at least afew will end in a favorable place for growth. Herbaceous perennials and woody plantsoften have larger seeds, they can produce seeds over many years, and larger seeds havemore energy reserves for germination and seedling growth and produce larger, moreestablished seedlings after germination.[4][5]Seed functionsSeeds serve several functions for the plants that produce them. Key among thesefunctions are nourishment of the embryo, dispersal to a new location, and dormancyduring unfavorable conditions. Seeds fundamentally are a means of reproduction andPlant anatomy, From Wikipedia, the free encyclopedia 132
  • 133. most seeds are the product of sexual reproduction which produces a remixing of geneticmaterial and phenotype variability that natural selection acts on.Embryo nourishmentSeeds protect and nourish the embryo or baby plant. Seeds usually give a seedling a fasterstart than a sporling from a spore gets because of the larger food reserves in the seed.Seed dispersal Main article: Biological dispersalUnlike animals, plants are limited in their ability to seek out favorable conditions for lifeand growth. As a consequence, plants have evolved many ways to disperse their offspringby dispersing their seeds (see also vegetative reproduction). A seed must somehow"arrive" at a location and be there at a time favorable for germination and growth. Whenthe fruits open and release their seeds in a regular way, it is called dehiscent, which isoften distinctive for related groups of plants, these fruits include; Capsules, follicles,legumes, silicles and siliques. When fruits do not open and release their seeds in a regularfashion they are called indehiscent, which include these fruits; Achenes, caryopsis, nuts,samaras, and utricles.[6]Seed dispersal is seen most obviously in fruits; however many seeds aid in their owndispersal. Some kinds of seeds are dispersed while still inside a fruit or cone, which lateropens or disintegrates to release the seeds. Other seeds are expelled or released from thefruit prior to dispersal. For example, milkweeds produce a fruit type, known as afollicle,[7] that splits open along one side to release the seeds. Iris capsules split into three"valves" to release their seeds.[8]By wind (anemochory)Dandelion seeds (achenes) can be carried long distances by the wind. • Many seeds (e.g. maple, pine) have a wing that aids in wind dispersal. • The dustlike seeds of orchids are carried efficiently by the wind. • Some seeds, (e.g. dandelion, milkweed, poplar) have hairs that aid in wind dispersal.By water (hydrochory) • Some plants, such as Mucuna and Dioclea, produce buoyant seeds termed sea- beans or drift seeds because they float in rivers to the oceans and wash up on beaches.[9]By animals (zoochory) • Seeds (burrs) with barbs or hooks (e.g. acaena, burdock, dock) which attach to animal fur or feathers, and then drop off later.Plant anatomy, From Wikipedia, the free encyclopedia 133
  • 134. • Seeds with a fleshy covering (e.g. apple, cherry, juniper) are eaten by animals (birds, mammals) which then disperse these seeds in their droppings. • Seeds (nuts) which are an attractive long-term storable food resource for animals (e.g. acorns, hazelnut, walnut); the seeds are stored some distance from the parent plant, and some escape being eaten if the animal forgets them.Myrmecochory is the dispersal of seeds by ants. Foraging ants disperse seeds whichhave appendages called elaiosomes[10] (e.g. bloodroot, trilliums, Acacias, and manyspecies of Proteaceae). Elaiosomes are soft, fleshy structures that contain nutrients foranimals that eat them. The ants carry such seeds back to their nest, where the elaiosomesare eaten. The remainder of the seed, which is hard and inedible to the ants, thengerminates either within the nest or at a removal site where the seed has been discardedby the ants.[11] This dispersal relationship is an example of mutualism, since the plantsdepend upon the ants to disperse seeds, while the ants depend upon the plants seeds forfood. As a result, a drop in numbers of one partner can reduce success of the other. InSouth Africa, the Argentine ant (Linepithema humile) has invaded and displaced nativespecies of ants. Unlike the native ant species, Argentine ants do not collect the seeds ofMimetes cucullatus or eat the elaiosomes. In areas where these ants have invaded, thenumbers of Mimetes seedlings have dropped.[12]Seed dormancy and protection Further information: Seed hibernationOne important function of most seeds is delaying germination, which allows time fordispersal and prevents germination of all the seeds at one time. The staggering ofgermination safeguards some seeds and seedlings from suffering damage or death fromshort periods of bad weather or from transient herbivores, it also allows some togerminate when competition from other plants for light and water might be less. Manyspecies of plants have seeds that germinate over many months or years, and some seedscan remain in the soil seed bank for more than 50 years before germination. Some seedhave a very long viability period, with the oldest documented germinating seed carbondated to be 2000 years old.[13] Seed dormancy is defined as a seed failing to germinateunder environmental conditions optimal for germination, normally when the environmentis at a suitable temperature with proper soil moisture. Induced dormancy or seedquiescence occurs when a seed fails to germinate because the external environmentalconditions are inappropriate for germination, mostly in response to being too cold or hot,or too dry. True dormancy or innate dormancy is caused by conditions within the seedthat prevent germination under normally ideal conditions. Often seed dormancy isdivided into four major categories: exogenous; endogenous; combinational; andsecondary.Exogenous dormancy is caused by conditions outside the embryo including: • Hard seed coats or physical dormancy occurs when seeds are impermeable to water or the exchange of gases. In some seeds the seed coat physically prevents the seedling from growing. • Chemical dormancy includes growth regulators etc.Endogenous dormancy is caused by conditions within the embryo itself, including: • Immature embryos where some plants release their seeds before the tissues of the embryos have fully differentiated, and the seeds ripen after they take in waterPlant anatomy, From Wikipedia, the free encyclopedia 134
  • 135. while on the ground, germination can be delayed from a few weeks to a few months. • Morphological dormancy where seeds have fully differentiated embryos that need to grow more before seed germination, the embryos are not yet fully developed. • Morphophysiological dormancy seeds with underdeveloped embryos, and in addition have physiological components to dormancy. These seeds therefore require a dormancy-breaking treatments as well as a period of time to develop fully grown embryos. • Physiological dormancy prevents seed germination until the chemical inhibitors are broken down or are no longer produced by the seed, often physiological dormancy is broken by a period of cool moist conditions, normally below (+4C) 39F, or in the case of many species in Ranunculaceae and a few others,(-5C) 24F. Other chemicals that prevent germination are washed out of the seeds by rainwater or snow melt. Abscisic acid is usually the growth inhibitor in seeds and its production can be affected by light. Some plants like Peony species have multiple types of physiological dormancy, one affects radical growth while the other affects shoot growth. o Drying; some plants including a number of grasses and those from seasonally arid regions need a period of drying before they will germinate, the seeds are released but need to have a lower moister content before germination can begin. If the seeds remain moist after dispersal, germination can be delayed for many months or even years. Many herbaceous plants from temperate climate zones have physiological dormancy that disappears with drying of the seeds. Other species will germinate after dispersal only under very narrow temperature ranges, but as the seeds dry they are able to germinate over a wider temperature range.[14] o Photodormancy or light sensitivity affects germination of some seeds. These photoblastic seeds need a period of darkness or light to germinate. In species with thin seed coats, light may be able to penetrate into the dormant embryo. The presence of light or the absence of light may trigger the germination process, inhibiting germination in some seeds buried too deeply or in others not buried in the soil. o Thermodormancy is seed sensitivity to heat or cold. Some seeds including cocklebur and amaranth germinate only at high temperatures (30C or 86F) many plants that have seed that germinate in early to mid summer have thermodormancy and germinate only when the soil temperature is warm. Other seeds need cool soils to germinate, while others like celery are inhibited when soil temperatures are too warm. Often thermodormancy requirements disappear as the seed ages or dries.Combinational dormancy also called double dormancy. Many seeds have more than onetype of dormancy,[15] some Iris species have both hard impermeable seeds coats andphysiological dormancy.Secondary dormancy is caused by conditions after the seed has been dispersed and occursin some seeds when non-dormant seed is exposed to conditions that are not favorable toPlant anatomy, From Wikipedia, the free encyclopedia 135
  • 136. germination, very often high temperatures. The mechanisms of secondary dormancy arenot yet fully understood but might involve the loss of sensitivity in receptors in theplasma membrane.[16]Many garden plants have seeds that will germinate readily as soon as they have water andare warm enough, though their wild ancestors may have had dormancy, these cultivatedplants lack seed dormancy. After many generations of selective pressure by plantbreeders and gardeners dormancy has been selected out.For annuals, seeds are a way for the species to survive dry or cold seasons. Ephemeralplants are usually annuals that can go from seed to seed in as few as six weeks.[17]Not all seeds undergo a period of dormancy. Seeds of some mangroves are viviparous,they begin to germinate while still attached to the parent. The large, heavy root allows theseed to penetrate into the ground when it falls.Seed germinationGerminating sunflower seedlings. Main articles: Seedling and GerminationSeed germination is the process of growth of the embryo into a functional plant. Itinvolves the reactivation of the metabolic pathways that lead to growth and theemergence of the radicle or seed root and plumule or shoot.Three fundamental conditions must exist before germination can occur. (1) The embryomust be alive, called seed viability. (2) Any dormancy requirements that preventgermination must be over come. (3) The proper environmental conditions must exist forgermination.Seed viability determines the percentage of possible seed germination and is affected by anumber of different conditions. Some plants do not produce seeds that have functionalcomplete embryos or the seed may have no embryo at all, often called empty seeds.Predators and pathogens can damage or kill the seed while it is still in the fruit or after itis dispersed. Environmental conditions like flooding or heat can kill the seed before orduring germination. The age of the seed affects its health and germination ability: sincethe seed has a living embryo, over time cells die and cannot be replaced. Some seeds canlive for a long time before germination, while others can only survive for a short periodafter dispersal before they die.Seed vigor is a measure of the quality of seed, and involves the viability of the seed, thegermination percentage, germination rate and the strength of the seedlings produced.[18]The germination percentage is simply the proportion of seeds that germinate from allseeds subject to the right conditions for growth. The germination rate is the length oftime it takes for the seeds to germinate. Germination percentages and rates are affectedby seed viability, dormancy and environmental effects that impact on the seed andPlant anatomy, From Wikipedia, the free encyclopedia 136
  • 137. seedling. In agriculture and horticulture quality seeds have high viability, measured bygermination percentage plus the rate of germination. This is given as a percent ofgermination over a certain amount of time, 90% germination in 20 days, for example.Dormancy is covered above; many plants produce seeds with varying degrees ofdormancy, and different seeds from the same fruit can have different degrees ofdormancy.[19] Its possible to have seeds with no dormancy if they are dispersed rightaway and do not dry (if the seeds dry they go into physiological dormancy). There isgreat variation amongst plants and a dormant seed is still a viable seed even though thegermination rate might be very low.Environmental conditions effecting seed germination include; water, oxygen, temperatureand light.Three distinct phases of seed germination occur: water imbibition; lag phase; and radicleemergence.In order for the seed coat to split, the embryo must imbibe (soak up water), which causesit to swell, splitting the seed coat. However, the nature of the seed coat determines howrapidly water can penetrate and subsequently initiate germination. The rate of imbibitionis dependent on the permeability of the seed coat, amount of water in the environmentand the area of contact the seed has to the source of water. For some seeds, imbibing toomuch water too quickly can kill the seed. For some seeds, once water is imbibed thegermination process cannot be stopped, and if the seed dries out again it is fatal. Otherspecies have seeds that can imbibe and lose water a few times without causing ill effectsto the seed, and drying can cause secondary dormancy.Inducing germinationA number of different strategies are used by gardeners and horticulturists to break seeddormancy.Scarification which allows water and gases to penetrate into the seed, include methodsthat physical break the hard seed coats or soften them by chemicals. Means ofscarification include soaking in hot water or poking holes in the seed with a pin orrubbing them on sandpaper or cracking with a press or hammer. Soaking the seeds insolvents or acids is also effective for many seeds. Sometimes fruits are harvested whilethe seeds are still immature and the seed coat is not fully developed and sown right awaybefore the seed coat become impermeable. Under natural conditions seed coats are worndown by rodents chewing on the seed, the seeds rubbing against rocks (seeds are movedby the wind or water currents), by undergoing freezing and thawing of surface water, orpassing through an animals digestive tract. In the latter case, the seed coat protects theseed from digestion, while often weakening the seed coat such that the embryo is ready tosprout when it gets deposited (along with a bit of fertilizer) far from the parent plant.Microorganisms are often effective in breaking down hard seed coats and are sometimesused by people as a treatment, the seeds are stored in a moist warm sandy medium forseveral months under non-sterile conditions.Stratification also called moist-chilling is a method to break down physiologicaldormancy and involves the addition of moisture to the seeds so they imbibe water andthen the seeds are subject to a period of moist chilling to after-ripen the embryo. Sowingoutside in late summer and fall and allowing to overwinter outside under cool conditionsis an effective way to stratify seeds, some seeds respond more favorably to periods ofosculating temperatures which are part of the natural environment.Plant anatomy, From Wikipedia, the free encyclopedia 137
  • 138. Leaching or the soaking in water removes chemical inhibitors in some seeds that preventgermination. Rain and melting snow naturally accomplish this task. For seeds planted ingardens, running water is best - if soaked in a container, 12 to 24 hours of soaking issufficient. Soaking longer, especially in stagnant water that is not changed, can result inoxygen starvation and seed death. Seeds with hard seed coats can be soaked in hot waterto break open the impermeable cell layers that prevent water intake.Other methods used to assist in the germination of seeds that have dormancy includeprechilling, predrying, daily alternation of temperature, light exposure, potassium nitrate,the use of plant growth regulators like gibberellins, cytokinins, ethylene, thiourea, sodiumhypochlorite plus others.[20] Some seeds germinate best after a fire, for some seeds firecrakes hard seed coats while in other seeds chemical dormancy is broken in reaction tothe presence of smoke, liquid smoke is often used by gardeners to assist in thegermination of these species.[21]Origin and evolutionThe origin of seed plants is a problem that still remains unsolved. However, more andmore data tends to place this origin in the middle Devonian. The description in 2004 ofthe proto-seed Runcaria heinzelinii in the Givetian of Belgium is an indication of thatancient origin of seed-plants. As with modern ferns, most land plants before this timereproduced by sending spores into the air, that would land and become whole new plants.The first "true" seeds are described from the upper Devonian, which is probably thetheater of their true first evolutionary radiation. The seed plants progressively becameone of the major elements of nearly all ecosystems.Economic importanceA variety of bean seeds.Edible seeds Further information: List of edible seedsMany seeds are edible and the majority of human calories comes from seeds, especiallyfrom cereals, legumes and nuts. Seeds also provide most cooking oils, many beveragesand spices and some important food additives. In different seeds the seed embryo or theendosperm dominates and provides most of the nutrients. The storage proteins of theembryo and endosperm differ in their amino acid content and physical properties. Forexample the gluten of wheat, important in providing the elastic property to bread dough isstrictly an endosperm protein.Seeds are used to propagate many crops such as cereals, legumes, forest trees, turfgrassesand pasture grasses.Plant anatomy, From Wikipedia, the free encyclopedia 138
  • 139. Seeds are also eaten by animals, and are fed to livestock. Many seeds are used asbirdseed.Poison and food safetyWhile some seeds are considered by some as healthy to eat, other seeds may be harmfulor poisonous,[22] Plants and seeds often contain chemical compounds to discourageherbivores and seed predators. In some cases, these compounds simply taste bad (such asin mustard), but other compounds are toxic, or breakdown into toxic compounds withinthe digestive system. Children, being smaller than adults, are more susceptible topoisoning or death by plants and seeds.[23] One should be satisfied with reliable foodsafety information before choosing to eat any particular seeds.An infamously deadly poison, ricin, comes from seeds of the castor bean. Reported lethaldoses are anywhere from two to eight seeds,[24][25] though only a few deaths have beenreported when castor beans have been ingested by animals.[26]In addition, seeds containing amygdalin; apple, apricot, bitter almond,[27] peach, plum,cherry, quince, and others, when consumed in significant amounts, may result in cyanidetoxicity[27].[28] Other seeds than contain poisons include annona, cotton, custard apple,datura, uncooked durian, golden chain, horse-chestnut, larkspur, locoweed, lychee,nectarine, rambutan, rosary pea, sour sop, sugar apple, wisteria, and yew.[29][30] Anotherseed poison is strychnine.The seeds of many legumes, including the common bean (Phaseolus vulgaris) containproteins called lectins which can cause gastric distress if the beans are eaten withoutcooking. The common bean and many others, including the soybean, also contain trypsininhibitors which interfere with the action of the digestive enzyme trypsin. Normalcooking processes degrade lectins and trypsin inhibitors to harmless forms.[31]Other usesFlax seed oil (in bottles) and coconut oil (in jars in the middle).The worlds most important clothing fiber grows attached to cotton seed. Other seedfibers are from kapok and milkweed.Many important nonfood oils are extracted from seeds. Linseed oil is used in paints. Oilfrom jojoba and crambe are similar to whale oil.Seeds are the source of some medicines including castor oil, tea tree oil and thediscredited cancer drug, Laetrile.Many seeds have been used as beads in necklaces and rosaries including Jobs tears,Chinaberry and rosary pea. However, the latter two are also poisonous.Other seed uses include: • Seeds once used as weights for balances.Plant anatomy, From Wikipedia, the free encyclopedia 139
  • 140. • Seeds used as toys by children, such as for the game conker. • Resin from Clusia rosea seeds used to caulk boats. • Nematicide from milkweed seeds. • Cottonseed meal used as animal feed and fertilizer.TriviaThe massive fruit of the coco de mer. • The oldest viable carbon-14-dated seed that has grown into a plant was a Judean date palm seed about 2,000 years old, recovered from excavations at Herod the Greats palace on Masada in Israel. It was germinated in 2005. [32] • The largest seed is produced by the coco de mer, or "double coconut palm", Lodoicea maldivica. The entire fruit may weigh up to 23 kilograms (50 pounds) and usually contains a single seed.[33] • The earliest fossil seeds are around 365 million years old from the Late Devonian of West Virginia. The seeds are preserved immature ovules of the plant Elkinsia polymorpha.[34]See also Biology portal • Biological dispersal • Germination • List of edible seeds • Recalcitrant seed • Seed company • Seed orchard • Seed predation • Seedbed • Seedling • StratificationReferences 1. ^ Kigel, Jaime, and Gad Galili. 1995. Seed development and germination. Books in soils, plants, and the environment. New York: M. Dekker.ISBN 0824792297. Chapter one. 2. ^ Raven, Peter H., Ray Franklin Evert, and Helena Curtis. 1981. Biology of plants. New York, N.Y.: Worth Publishers. page 410.Plant anatomy, From Wikipedia, the free encyclopedia 140
  • 141. 3. ^ Smith, Welby R. 1993. Orchids of Minnesota. Minneapolis: University of Minnesota Press. Page 8. 4. ^ Igor Kosinki. "Long-term variability in seed size and seedling establishment of Maianthemum bifolium". Plant Ecology 194 (2): 149-156. 5. ^ Assessment of hedgerow species for seed size, stand establishment and seedling height 6. ^ Jones, Samuel B., and Arlene E. Luchsinger. 1979. Plant systematics. McGraw-Hill series in organismic biology. New York: McGraw-Hill. Page 195. 7. ^ Cronquist, Arthur (1981). An Integrated System of Classification of Flowering Plants. New York: Columbia University Press, 882. ISBN 0-231-03880-1. 8. ^ Stern, Kingsley R. (1991). Introductory Plant Biology, 5th, Dubuque, IA: Wm. C. Brown Publishers, 131. ISBN 0-697-09947-4. 9. ^ http://www.seabean.com/ 10. ^ Marinelli, J. (1999) "Ants - The astonishing intimacy between ants & plants." Plants & Gardens News 14 (1). [1] 11. ^ Ricklefs, Robert E. (1993) The Economy of Nature, 3rd ed., p.396. (New York: W. H. Freeman). ISBN 0-7167-2409-X. 12. ^ Bond, W. J.; P. Slingsby (1984). "Collapse of an ant-plant mutualism: The Argentine ant, Iridomyrmex humilis and myrmecochorous Proteaceae". Ecology 65: 1031–1037. doi:10.2307/1938311. 13. ^ RANDOLPH E. SCHMID, Tree from 2,000-year-old seed is doing well. AP, Jun 12, 2008 14. ^ International Workshop on Seeds, and G. Nicolas. 2003. The biology of seeds recent research advances : proceedings of the Seventh International Workshop on Seeds, Salamanca, Spain 2002. Wallingford, Oxon, UK: CABI Pub. Page 113. 15. ^ The Seed Biology Place - Seed Dormancy 16. ^ Bewley, J. Derek, and Michael Black. 1994. Seeds physiology of development and germination. The language of science. New York: Plenum Press. page 230. 17. ^ Patten, D.T. 1978. Productivity and production efficiency of an Upper Sonoran Desert ephemeral community. American Journal of Botany 65: 891-895. 18. ^ Seed Vigor and Vigor Tests 19. ^ International Seed Testing Association. 1973. ISSN 0251-0952. Pages 120-21.Seed science and technology. Wageningen?: International Seed Testing Association. 20. ^ Hartmann, Hudson Thomas, and Dale E. Kester. 1983. Plant propagation principles and practices. Englewood Cliffs, N.J.: Prentice-Hall. ISBN 0136810071. Pages 175-77. 21. ^ Trace Gas Emissions and Smoke-Induced Seed Germination - Keeley and Fotheringham 276 (5316): 1248 - Science 22. ^ Chia Joo Suan, "Seeds of Doubt: Food Safety" 23. ^ Clelland, Mike. "Poisonous Plants and Seeds", Healthy Child Care 24. ^ Poisonous Plants 25. ^ Wedin GP, Neal JS, Everson GW, Krenzelok EP. Castor bean poisoning. 26. ^ Albretsen JC, Gwaltney-Brant SM, Khan SA. Evaluation of castor bean toxicosis in dogs: 98 cases. 27. ^ a b Almond/Almond Oil 28. ^ Wolke, RL. Seeds of Anxiety Washington Post January 5, 2005 29. ^ Poisonous plants 30. ^ Chia Joo Suan Food Safety: Seeds of doubt 31. ^ N.V. DHURANDHAR, K.C. CHANG (1990) Effect of Cooking on Firmness, Trypsin Inhibitors, Lectins and Cystine/Cysteine content of Navy and Red Kidney Beans (Phaseolus vulgaris) Journal of Food Science 55 (2), 470–474. 32. ^ Roach, John. (2005) "2,000-Year-Old Seed Sprouts, Sapling Is Thriving", National Geographic News, 22 November.Plant anatomy, From Wikipedia, the free encyclopedia 141
  • 142. 33. ^ Corner, E. J. H. (1966) The Natural History of Palms, p313-314. (Berkeley, CA: University of California Press). 34. ^ Taylor, Thomas N. & Edith L. Taylor. 1993 The Biology and Evolution of Fossil Plants, page 466. (Englewood Cliffs, NJ: Prentice Hall). ISBN 0-13-651589-4.External links Wikimedia Commons has media related to: SeedLook up seed inWiktionary, the free dictionary. • List of Common Botanical Seed Names • The Seed Site: collecting, storing, sowing, germinating, and exchanging seeds, with pictures of seeds, seedpods and seedlings. • The Seed Biology Place seed structure, dormany, evolution, ecology, etc. • Flavons Secret Flower Garden - Pictures of Japanese plant seeds, fruits and etc. • The Millennium Seed Bank Project Kew Gardens ambitious preservation project • The Svalbard Global Seed Vault - a backup facility for the worlds seed banksBiological dispersalWind dispersal of dandelion seeds.Biological dispersal refers to those processes by which a species maintains or expandsthe distribution of a population. Dispersal implies movement—movement away from anexisting population (population expansion) or away from the parent organism (populationmaintenance). This is necessary for members of a population because organisms of thesame age require all of the same resources within an ecosystem. Dispersal relievespressure for resources in an ecosystem, and competition for these resources may be aselection factor for dispersal mechanisms.[1]In the latter case, dispersal may simply involve replacement of the parent generation bythe new generation, with only minor changes in geographic area occupied.In most cases, organisms (plants and especially sedentary animals) have evolvedadaptations for dispersal that take advantage of various forms of kinetic energy occurringnaturally in the environment: water flow, wind, falling (response to gravity).Dispersal of organisms is a critical process for understanding both geographic isolation inevolution and the broad patterns of current geographic distributions.Plant anatomy, From Wikipedia, the free encyclopedia 142
  • 143. Contents[hide] • 1 Of plants o 1.1 Gravity o 1.2 Mechanical o 1.3 Wind o 1.4 Water o 1.5 By animals • 2 Of animals o 2.1 Non-motile animals o 2.2 Motile animals • 3 See also • 4 References • 5 Further reading • 6 External linksOf plantsUnlike animals, plants are limited in their ability to seek out favorable conditions for lifeand growth. Consequently, plants have evolved many ways to disperse and spread apopulation through their seeds or spores (see also vegetative reproduction). Thoseproperties or attributes that promote the movement of the next generation away from theparent plant may involve the fruit more so than the seeds themselves.GravityThe effect of gravity on the dispersal of seeds and spores is simple: heavy seeds dropdownward from the parent plant, though not very far by themselves. Encasing seeds in arounded fruit promotes gravity driven movement away from the parent. Spores, beingmuch lighter, are more influenced by physical movements in the environment, especiallythose of wind and water, and therefore less strictly subject to gravity alone. Gravity maybe sufficient agent for plants growing on steep slopes, but upslope movement of apopulation can be a problem. Plants such as gymnosperms that utilize gravity fordispersal often rely on additional dispersal adaptations favoring zoochory or anemochory;few rely on gravity alone.MechanicalThe fruit of the squirting cucumber (Ecballium elaterium) releases its seeds in a powerfuljet of liquid.Numerous species have evolved mechanical means to overcome the tendency of a seed todrop close to its parent. Seedpods are often shaped so that the seeds are flung away fromthe parent plant with considerable force as the seedpod matures.Plant anatomy, From Wikipedia, the free encyclopedia 143
  • 144. Examples of fruit with mechanical dispersal mechanisms: • Oxalis corniculata – capsule, as it dries, becomes sensitive to disturbance, ejecting tiny seeds in an explosive discharge. • Narrow-leaf Bittercress [2] • LegumesWindAnemochory, or wind dispersal, is probably the most primitive form of dispersal besidesgravity alone. Wind is reliable, but plants must produce seeds to ensure that a sufficientnumber will land by chance in a suitable location, making anemochory an inefficientmeans of dispersal. Wind dispersal is common among ruderal species, including someimportant agricultural and horticultural weeds such as hawkweed, horseweed, anddandelion. Like many members of the Asteraceae, or sunflower family, they produceseeds with a feathery "parachute" called a pappus that aids wind dispersal,allowing themto be carried over distances. Wikimedia Commons has media related to: Wishie WaterPlants that grow in water (aquatic and obligate wetland species) are likely to utilize waterto disperse their seeds. For example, all mangroves disperse their offspring by water.Hydrochory is the dispersal of seeds by water; a plant which uses this method in its lifecycle is termed a hydrochore. Rhizophora demonstrates an unorthodox method ofpropagation called vivipary: the embryo is retained on the plant until after germination; inessence, a dry seed is not produced. The hypocotyl of the germinating seedling (nowcalled a propagule) bursts through the fruit and hangs, poised for continued growth. In R.mangle, the hypocotyl can reach a length of 20 to 25 cm; and in R. mucronata lengths upto 1 m have been recorded. Eventually, the seedling separates from the fruit, leaving itscotyledons behind, and—floating horizontally on the water surface—is carried away bytidal or river flow. After a month or two, the propagule turns vertical in the water. Oncethe hypocotyl of a propagule "feels" bottom or strands, roots start to develop and leavesappear at the upper end (Hogarth, 1999).Adaptations commonly seen in littoral plants are those that promote flotation of the fruit,allowing the seed to be carried away on the tide or ocean currents. Examples would be: • Cocos nucifera – the coconut produces a large, dry, fiber-filled fruit (a fibrous drupe) capable of a long survival adrift at sea. • Calophyllum inophyllum – Alexandrian laurel or kamani produces a globose fruit that is almost cork-like.Terrestrial plants may also have their seeds dispersed by raindrops. By animals A barbed seed caught in the fur of a cat. Many plants rely on zoochory, dispersal by animals. Animal dispersal is broadly divided into two categories: endozoochory, transport internally, and epizoochory, external transport. Endozoochory is generally a coevolvedPlant anatomy, From Wikipedia, the free encyclopedia 144
  • 145. mutualistic relationship in which a plant surrounds seeds with an edible, nutritious fruit asa reward to animals that consume it. Seeds within the fruit are often protected by toughouter coating; many seeds have such thick protection that they cannot germinate untilthey are scarified by digestion. This keeps the seed from sprouting while still in the fruitand reduces competition with the parent plant. Birds and mammals are the mostimportant seed dispersers, but a wide variety of other animals, such as box turtles[3][4] andfish[5] can transport viable seeds. Some animals that disperse may also eat the seed. Manyrodents (such as squirrels) hoard seeds in hidden caches; those left uneaten can grow intoa new plant.Epizoochory, or transport on the outside of an animal, is often a commensalisticrelationship in which the plant benefits but the animal does not. Plants such as burdockand cocklebur have fruits with recurving hairs or spikes that cling to fur or feathers sothat passing animals will carry them away. Many species in the genus Bidens are called"beggars ticks" because their achenes stick in clothes using special barbed awns. Manymembers of the Apiaceae (carrot family) such as Torilis, Caucalis, and Daucus havespikes or spiky hairs on their fruits.Of animalsMost (but not all) animals are capable of locomotion and the basic mechanism ofdispersal is movement from one place to another. Locomotion allows the organism to"test" new environments for their suitability, provided they are within animals range.Movements are usually guided by inherited behaviors.Non-motile animalsThere are numerous animal forms that are non-motile, such as sponges, bryozoans,tunicates, sea anemones, corals, and oysters. In common, they are all either marine oraquatic. It may seem curious that plants have been so successful at stationary life on land,while animals have not, but the answer lies in the food supply. Plants produce their ownfood from sunlight and carbon dioxide—both generally more abundant on land than inwater. Animals fixed in place must rely on the surrounding medium to bring food at leastclose enough to grab, and this occurs in the three-dimensional water environment, butwith much less abundance in the atmosphere. However, that such a life form might bepossible is at least suggested by the orb-weaver spiders.All of the marine and aquatic invertebrates whose lives are spent fixed to the bottom(more or less; anemones are capable of getting up and moving to a new location ifconditions warrant) produce dispersal units. These may be specialized "buds", or motilesexual reproduction products, or even a sort of alteration of generations as in certaincnidaria.Corals provide a good example of how sedentary species achieve dispersion. Coralsreproduce by releasing sperm and eggs directly into the water. These release events arecoordinated by lunar phase in certain warm months, such that all corals of one or manyspecies on a given reef will release on the same single or several consecutive nights. Thereleased eggs are fertilized, and the resulting zygote develops quickly into a multicellularplanula. This motile stage then attempts to find a suitable substratum for settlement.Most are unsuccessful and die or are fed upon by zooplankton and bottom dwellingpredators such as anemones and other corals. However, untold millions are produced, anda few do succeed in locating spots of bare limestone, where they settle and transform byPlant anatomy, From Wikipedia, the free encyclopedia 145
  • 146. growth into a polyp. All things being favorable, the single polyp grows into a coral headby budding off new polyps to form a colony.Motile animalsAlthough motile animals can, in theory, disperse themselves by their locomotive powers,a great many species utilize the existing kinetic energies in the environment. Dispersal bywater currents is especially associated with the physically small inhabitants of marinewaters known as zooplankton. The term plankton comes from the Greek, πλαγκτον,meaning "wanderer" or "drifter".See also • Dormancy - dispersal in time • Gene flowReferences 1. ^ Irwini, AJ; PD Taylor (2000). "Evolution of Dispersal in a Stepping-Stone Population with Overlapping Generations". Theoretical Population Biology 58: 321 328. Academic Press. doi:10.1006/tpbi.2000.1490. Retrieved on 2007-08- 07. 2. ^ Dispersal 3. ^ Seed Production and Seedling Establishment in the Mayapple, Podophyllum peltatum L., by R.W. Rust and R.R. Roth. 1909. The American Midland Naturalist, University of Notre Dame. 4. ^ Hong Liu, Steven G. Platt, and Christopher K. Borg. 2004. Seed dispersal by the Florida box turtle (Terrapene carolina bauri) in pine rockland forests of the lower Florida Keys, United States. Oecologia Volume 138, Number 4 5. ^ POLLUX, B. J. A.; OUBORG, N. J.; VAN GROENENDAEL, J. M.; KLAASSEN, M. 2007. Consequences of intraspecific seed-size variation in Sparganium emersum for dispersal by fish. Functional Ecology, Volume 21, Number 6 • Hogarth, Peter J. 1999. The Biology of Mangroves. Oxford Univ. Press. 228 p. ISBN 0-19-850222-2Further reading • Ingold, C. T. (1971) Fungal spores: their liberation and dispersal Oxford, Clarendon Press 302 p. ISBN 0198541155 • Lidicker, W. Z. and R. L. Caldwell (1982) Dispersal and migration Stroudsburg, Pa. : Hutchinson Ross Pub. Co 311 p. ISBN 0879334355 (Dispersal of animals) • Bullock, J. M.; R. E. Kenward, and R. S. Hails (editors) (2002) Dispersal ecology : the 42nd symposium of the British Ecological Society. Oxford, UK : Blackwell Science 458 p. ISBN 0632058765 (Animals and plants)External links • Fruit and seed dispersal images at bioimages.vanderbilt.edu • Interactive model of movement of plant species induced by climate changeRetrieved from "http://en.wikipedia.org/wiki/Biological_dispersal"Plant anatomy, From Wikipedia, the free encyclopedia 146
  • 147. GerminationNot to be confused with Gemination inphonetics.Sunflower seedlings, just three days aftergermination Germination rate testing on the germination table Germination is the process whereby growth emerges from a period of dormancy. The most common example of germination is the sproutingof a seedling from a seed of an angiosperm or gymnosperm. However, the growth of asporeling from a spore, for example the growth of hyphae from fungal spores, is alsogermination. In a more general sense, germination can imply anything expanding intogreater being from a small existence or germ.Contents • 1 Seed germination o 1.1 Requirements for seed germination o 1.2 Dormancy o 1.3 Seedling establishment • 2 Germination rate o 2.1 Dicot germination 2.1.1 Epigeous 2.1.2 Hypogeous o 2.2 Monocot germination o 2.3 Precocious germination • 3 Pollen germination o 3.1 Self-incompatibility • 4 Spore germination o 4.1 Resting spores o 4.2 Zoospores o 4.3 Ferns and mosses • 5 See also • 6 ReferencesPlant anatomy, From Wikipedia, the free encyclopedia 147
  • 148. 7 External linksSeed germinationBrassica campestris germinating seedsA germinated seedling (Eranthis hyemalis) emerges from the groundGermination is the growth of an embryonic plant contained within a seed, it results in theformation of the seedling. The seed of a higher plant is a small package produced in afruit or cone after the union of male and female sex cells. Most seeds go through a periodof quiescences where there is no active growth, during this time the seed can be safelytransported to a new location and/or survive adverse climate conditions until it isfavorable for growth. The seed contains an embryo and in most plants stored foodreserves wrapped in a seed coat. Under favorable conditions, the seed begins togerminate, and the embryonic tissues resume growth, developing towards a seedling.Requirements for seed germinationThe germination of seeds is dependent on both internal and external conditions. The mostimportant external factors include: temperature, water, oxygen and sometimes light ordarkness.[1] Often different varieties of seeds require distinctive variables for successfulgermination; some seeds germinate while the soil is cold, while most germinate while thesoil is warm. This depends on the individual seed variety and is closely linked to theecological conditions of the plants natural habitat. • Water - is required for germination. Mature seeds are often extremely dry and need to take in significant amounts of water, relative to the seeds dry weight, before cellular metabolism and growth can resume. Most seeds respond best when there is enough water to moisten the seeds but not soak them. The uptake of water by seeds is called imbibition which leads to the swelling and the breaking of the seed coat. When seeds are formed, most plants store food, such as starch, proteins, or oils, to provide nourishment to the growing embryo inside the seed. When thePlant anatomy, From Wikipedia, the free encyclopedia 148
  • 149. seed imbibes water, hydrolytic enzymes are activated that break down these stored food resources in to metabolically useful chemicals, allowing the cells of the embryo to divide and grow, so the seedling can emerge from the seed.[1] Once the seedling starts growing and the food reserves are exhausted, it requires a continuous supply of water, nutrients and light for photosynthesis, which now provides the energy needed for continued growth. [2] • Oxygen - is required by the germinating seed for metabolism: If the soil is waterlogged or the seed is buried within the soil, it might be cut off from the necessary oxygen it needs. Oxygen is used in aerobic respiration, the main source of the seedlings energy until it has leaves, which can photosynthesize its energy requirements.[1] Some seeds have impermeable seed coats that prevent oxygen from entering the seeds, causing seed dormancy. Impermeable seed coats to oxygen or water, are types of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange or water uptake between the seed and its surroundings. • Temperature - affects cellular metabolic and growth rates. Different seeds germinate over a wide range of temperatures, with many preferring temperatures slightly higher than room-temperature while others germinate just above freezing and others responding to alternation in temperature between warm to cool. Often, seeds have a set of temperature ranges where they will germinate and will not do so above or below this range. In addition, some seeds may require exposure to cold temperature (vernalization) to break dormancy before they can germinate. As long as the seed is in its dormant state, it will not germinate even if conditions are favorable. Seeds that are dependent on temperature to end dormancy, have a type of physiological dormancy. For example, seeds requiring the cold of winter are inhibited from germinating until they experience cooler temperatures. For most seeds that require cold for germination 4C is cool enough to end dormancy, but some groups especially with in the family Ranunculaceae and others, need less than -5C. Some seeds will only germinate when temperatures reach hundreds of degrees, as during a forest fire. Without fire, they are unable to crack their seed coats, this is a type of physical dormancy. • Light or darkness - can be a type of environmental trigger for germination in seeds and is a type of physiological dormancy. Most seeds are not affected by light or darkness, but many seeds, including species found in forest settings will not germinate until an opening in the canopy allows them to receive sufficient light for the growing seedling.[1]Stratification mimics natural processes that weaken the seed coat before germination. Innature, some seeds require particular conditions to germinate, such as the heat of a fire(e.g., many Australian native plants), or soaking in a body of water for a long period oftime. Others have to be passed through an animals digestive tract to weaken the seed coatand enable germination.[1]Plant anatomy, From Wikipedia, the free encyclopedia 149
  • 150. Malted (germinated) barley grainsDormancyMany live seeds have dormancy, meaning they will not germinate even if they have waterand it is warm enough for the seedling to grow. Dormancy factors include conditionsaffecting many different parts of the seed, from the embryo to the seed coat. Dormancy isbroken or ended by a number of different conditions and cues both internal and externalto the seed. Environmental factors like light, temperature, fire, ingestion by animals andothers are conditions that can end seed dormancy. Internally seeds can be dormantbecause of plant hormones such as absciscic acid, which affects seed dormancy andprevents germination, while the production and application of the hormone gibberellincan break dormancy and induces seed germination. This effect is used in brewing wherebarley is treated with gibberellin to ensure uniform seed germination to produce barleymalt.[1]Seedling establishmentIn some definitions, the appearance of the radicle marks the end of germination and thebeginning of "establishment", a period that ends when the seedling has exhausted thefood reserves stored in the seed. Germination and establishment as an independentorganism are critical phases in the life of a plant when they are the most vulnerable toinjury, disease, and water stress.[1] The germination index can be used as an indicator ofphytotoxicity in soils. The mortality between dispersal of seeds and completion ofestablishment can be so high, that many species survive only by producing huge numbersof seeds.Germination rateIn agriculture and gardening, germination rate is the number of seeds of a particularplant species, variety or particular seedlot that are likely to germinate. This is usuallyexpressed as a percentage, e.g. an 85% germination rate indicates that about 85 out of 100seeds will probably germinate under proper conditions. Germination rate is useful incalculating seed requirements for a given area or desired number of plants.Dicot germinationThe part of the plant that emerges from the seed first is the embryonic root, termedradicle or primary root. This allows the seedling to become anchored in the ground andstart absorbing water. After the root absorbs water, the embryonic shoot emerges fromthe seed. The shoot comprises three main parts: the cotyledons (seed leaves), the sectionPlant anatomy, From Wikipedia, the free encyclopedia 150
  • 151. of shoot below the cotyledons (hypocotyl), and the section of shoot above the cotyledons(epicotyl). The way the shoot emerges differs between plant groups.[1]EpigeousIn epigeous (or epigeal) germination, the hypocotyl elongates and forms a hook, pullingrather than pushing the cotyledons and apical meristem through the soil. Once it reachesthe surface, it straightens and pulls the cotyledons and shoot tip of the growing seedlingsinto the air. Beans, tamarind, and papaya are examples of plant that germinate this way.[1]HypogeousAnother way of germination is hypogeous (or hypogeal) where the epicotyl elongates andforms the hook. In this type of germination, the cotyledons stay underground where theyeventually decompose. Peas, for example, germinate this way.[1]Monocot germinationIn monocot seeds, the embryos radicle and cotyledon are covered by a coleorhiza andcoleoptile, respectively. The coleorhiza is the first part to grow out of the seed, followedby the radicle. The coleoptile is then pushed up through the ground until it reaches thesurface. There, it stops elongating and the first leaves emerge through an opening as itis.[1]Precocious germinationWhile not a class of germination, this refers to germination of the seed occurring insidethe fruit before it has begun to decay. The seeds of the green apple commonly germinatein this manner.[citation needed]Pollen germinationAnother germination event during the life cycle of gymnosperms and flowering plants isthe germination of a pollen grain after pollination. Like seeds, pollen grains are severelydehydrated before being released to facilitate their dispersal from one plant to another.They consist of a protective coat containing several cells (up to 8 in gymnosperms, 2-3 inflowering plants). One of these cells is a tube cell. Once the pollen grain lands on thestigma of a receptive flower (or a female cone in gymnosperms), it takes up water andgerminates. Pollen germination is facilitated by hydration on the stigma, as well as thestructure and physiology of the stigma and style.[1] Pollen can also be induced togerminate in vitro (in a petri dish or test tube).[3][4]During germination, the tube cell elongates into a pollen tube. In the flower, the pollentube then grows towards the ovule where it discharges the sperm produced in the pollengrain for fertilization. The germinated pollen grain with its two sperm cells is the maturemale microgametophyte of these plants.[1]Self-incompatibility Main article: Self-incompatibility in plantsSince most plants carry both male and female reproductive organs in their flowers, thereis a high risk for self-pollination and thus inbreeding. Some plants use the control ofpollen germination as a way to prevent this selfing. Germination and growth of the pollentube involve molecular signaling between stigma and pollen. In self-incompatibility inplants, the stigma of certain plants can molecularly recognize pollen from the same plantand prevents it from germinating.[5]Spore germinationGermination can also refer to the emergence of cells from resting spores and the growthof sporeling hyphae or thalli from spores in fungi, algae, and some plants.Plant anatomy, From Wikipedia, the free encyclopedia 151
  • 152. Conidia are the asexual reproductive spores of fungi, which germinate under specificconditions. From the germinating conidia different cells are formed. The most commonone is the germ tube. The germ tube will grow and developed into the hyphae. Duringgermination, conidial may produce conidial anastomosis tubes, those are different fromconidial anastomosis tubes because they are thinner, shorter, lack branches, exhibitdeterminate growth, and home toward each other. Both cells have a tubular shape, but theconidial anastomosis form a bridge that allows fusion between conidia. [6][7]Resting sporesIn resting spores, germination involves cracking the thick cell wall of the dormant spore.For example, in zygomycetes the thick-walled zygosporangium cracks open and thezygospore inside gives rise to the emerging sporangiophore. In slime molds, germinationrefers to the emergence of amoeboid cells from the hardened spore. After cracking thespore coat, further development involves cell division, but not necessarily thedevelopment of a multicellular organism (for example in the free-living amoebas of slimemolds).[1]ZoosporesIn motile zoospores, germination frequently means a lack of motility and changes in cellshape, which allow the organism to become sessile.[1]Ferns and mossesIn plants such as bryophytes, ferns, and a few others, spores germinate into independentgametophytes. In the bryophytes (e.g. mosses and liverworts), spores germinate intoprotonemata, similar to fungal hyphae, from which the gametophyte grows. In ferns, thegametophytes are small, heart-shaped prothalli that can often be found underneath aspore-shedding adult plant.[1]See also • Lily Seed Germination Types • Seedling • SproutingReferences 1. ^ a b c d e f g h i j k l m n o p Raven, Peter H.; Ray F. Evert, Susan E. Eichhorn (2005). Biology of Plants, 7th Edition. New York: W.H. Freeman and Company Publishers, 504-508. ISBN 0-7167-1007-2. 2. ^ S. M. Siegel, L. A. Rosen (1962) Effects of Reduced Oxygen Tension on Germination and Seedling Growth Physiologia Plantarum 15 (3) , 437–444 doi:10.1111/j.1399- 3054.1962.tb08047.x 3. ^ Martin FW (1972). "In Vitro Measurement of Pollen Tube Growth Inhibition". Plant Physiol 49 (6): 924–925. PMID 16658085. 4. ^ Pfahler PL (1981). "In vitro germination characteristics of maize pollen to detect biological activity of environmental pollutants". Environ. Health Perspect. 37: 125–32. doi:10.2307/3429260. PMID 7460877. 5. ^ Takayama S, Isogai A (2005). "Self-incompatibility in plants". Annu Rev Plant Biol 56: 467–89. doi:10.1146/annurev.arplant.56.032604.144249. PMID 15862104. 6. ^ Roca M., M.G.; Davide, L.C.; Davide, L.M.; Mendes-Costa, M.C.; Schwan, R.F.; Wheals, A. 2004. Conidial anastomoses fusions between Colletotrichum species. Mycological Research. 108, 11: 1320-1326. 7. ^ Roca, M.G.; Arlt, J., Jeffree, C.E.; Read, N.D. 2005. Cell biology of conidial anastomosis tubes in Neurospora crassa. Eukaryotic Cell 4: 911-919.Plant anatomy, From Wikipedia, the free encyclopedia 152
  • 153. External linksWikibooks has more on the topic ofGermination • Sowing Seeds A survey of seed sowing techniques. • Seed Germination: Theory and Practice, Norman C. Deno, 139 Lenor Dr., State College PA 16801, USA. An extensive study of the germination rates of a huge variety of seeds under different experimental conditions, including temperature variation and chemical environment.Retrieved from "http://en.wikipedia.org/wiki/Germination"Categories: Developmental biology | Plant reproductionHidden categories: All articles with unsourced statements | Articles with unsourcedstatements since December 2007List of edible seedsFrom Wikipedia, the free encyclopediaJump to: navigation, searchA list of edible seeds here includes seeds that are directly foodstuffs, rather than yieldingderived products.A variety of species can provide edible seeds. Of the six major plant parts, seeds are themost important source of human food. The other five major plant parts are roots, stems,leaves, flowers, and fruits. Most edible seeds are angiosperms, but a few aregymnosperms. The most important seed food source is cereals, followed by legumes, andnuts.The list is divided into the following categories: • Beans (or Legumes) are protein-rich soft seeds. • Cereals (or grains) are grass-like crops that are harvested for their dry seeds. These seeds are often ground to make flour. Cereals provide almost half of all calories consumed in the world.[1] Botanically, true cereals are members of the Poaceae or Grass family. o Pseudocereals are cereal crops that are not members of the Poaceae or Grass Family. • Nuts are botanically a specific type of fruit but the term is also applied to many edible seeds that are not botanically nuts. o Gymnosperms produce nut-like seeds but not flowers or fruits.Plant anatomy, From Wikipedia, the free encyclopedia 153
  • 154. Contents • 1 Beans • 2 Cereals o 2.1 Pseudocereals • 3 Nuts o 3.1 Nut-like gymnosperm seeds • 4 Miscellaneous • 5 References • 6 See alsoBeansSee also: Category:Edible legumesBeans, also known as legumes or pulses include:[2] Lentils have been part of the human diet since the Neolithic • Bambara groundnut • Chickpeas • Cowpeas • Dry beans, including o Common bean o several species of Vigna • Fava or broad beans • Hyacinth bean • Lablab • Lentils • Lupins • Peas • Peanuts • Pigeon peas • Velvet beans • Winged beans • Yam beans • Tonka beans • SoybeansCereals See also: Category:Cereals Corn is the single largest source of food calories in the world. True cereals are the seeds of certain species of grass. Three — maize, wheat and rice — account for about half of the calories consumed by people every year.[1] Grains can be ground to make flour, used as the basis ofbread, cake, noodles or other food products. They can also be boiled or steamed, eitherPlant anatomy, From Wikipedia, the free encyclopedia 154
  • 155. whole or ground, and eaten as is. Many cereals are present or past staple foods, provideda large fraction of the calories in the places that they are eaten. Cereals include: • Barley • Fonio • Kamut • Maize (corn) • Pearl Millet • Oats • Palmers grass • Rice • Rye • Sorghum • Spelt • Teff • Triticale • Wheat • Wild ricePseudocereals Quinoa is not a grass, but its seeds have been eaten for 6000 years. • Breadnut • Buckwheat • Cattail • Chia • Cockscomb • Grain amaranth • Kañiwa • Pitseed Goosefoot • Quinoa • Wattleseed (also called acacia seed)Nuts See also: List of edible nuts Brazil nuts come from a South American tree According to the botanical definition, nuts are a particular kind of seed.[3] Walnuts and acorns are example of nuts, under this definition. In culinary terms, however, the term is used more broadly to include fruitsthat are not botanically qualified as nuts, but that have a similar appearance and culinaryrole. Examples of culinary nuts include almonds, peanuts and cashews.[4][5] • Almond • Beech • Brazil nutPlant anatomy, From Wikipedia, the free encyclopedia 155
  • 156. • Candlenut • Cashew • Chestnuts, including: o Chinese Chestnut o Sweet Chestnut • Colocynth • Cucurbita ficifolia • Filbert • Gevuina avellana • Hickory, including o Pecan o Shagbark Hickory • Indian Beech or Pongam Tree • Kola nut • Macadamia • Malabar chestnut • Mamoncillo • Maya nut • Mongongo • Oak acorns • Ogbono nut • Paradise nut • Pili nut • Walnut • Water Caltrop Nut-like gymnosperm seeds Pine nuts are Gymnosperm seeds that are edible • Cycads • Ginkgo • Gnetum gnemon • Juniper • Monkey-puzzle • Pine nuts, including o Chilgoza Pine o Korean Pine o Stone Pine o Colorado Pinyon o Mexican Pinyon o Single-leaf Pinyon • PodocarpsMiscellaneous This article or section is in need of attention from an expert on the subject. WikiProject Plants or the Plants Portal may be able to help recruit one. If a more appropriate WikiProject or portal exists, please adjust this template accordingly.Plant anatomy, From Wikipedia, the free encyclopedia 156
  • 157. This article or section is in need of attention from an expert on the subject. WikiProject Biology or the Biology Portal may be able to help recruit one. If a more appropriate WikiProject or portal exists, please adjust this template accordingly. • Cempedak • Egusi • Euryale ferox (Fox nut) • Fluted pumpkin • Hemp seed • Jackfruit • Lotus seed • Malabar gourd • Pistachio • Pumpkin seed • Sunflower seedReferences 1. ^ a b FAO. "ProdSTAT". FAOSTAT. Retrieved on 2006-12-26. 2. ^ "Pulses and derived products". Definition and Classification of Commodities. Food and Agriculture Organization of the United Nations (1994). Retrieved on 2006-12-26. 3. ^ "Nut". Biology Online Dictionary (October 3, 2005). Retrieved on 2006-12-26. 4. ^ "Nut". The Columbia Online Encyclopedia (2003). Retrieved on 2006-12-26. 5. ^ "Nuts and derived products". Definition and Classification of Commodities. Food and Agriculture Organization of the United Nations (1996). Retrieved on 2006-12-26. • Bailey, L.H., Bailey, E.Z. and Bailey Hortorium Staff (1976). Hortus Third. New York: Macmillan. • Lewington, A. (1990). Plants for People. Cambridge, MA: Oxford University Press.See also • Eastern Agricultural Complex • List of vegetable oils • List of seed-based snacks • Nut (fruit) • Pulse • SeedRecalcitrant seedRecalcitrant seeds (sometimes known as unorthodox seeds) are seeds that do not survivedrying and freezing during ex-situ conservation.[1] Moreover, these seeds cannot resist theeffects of drying or temperatures less than 10° C thus they cannot be stored for longperiods like Orthodox seeds because they can lose their viability. Plants that producerecalcitrant seeds include avocado, mango, lychee, some horticultural trees, and severalplants used in traditional medicine.Plant anatomy, From Wikipedia, the free encyclopedia 157
  • 158. Mechanisms of damageThe two main mechanisms of action of damage to recalcitrant seeds are desiccation effecton the intracellular structures and the effect of metabolic damage from the formation oftoxic chemicals such as free radicals.[2] An example of the first type of damage would befound in some recalcitrant nontropical hardwood seeds, specifically the acorns ofrecalcitrant oaks, which can be stored in a nonfrozen state for up to two years providedthat precautions be taken against drying. These seeds showed deterioration of cellmembrane lipids and proteins after as few as 3-4 days of drying.[3] Other seeds such asthose of Castanea sativa - sweet chestnut show oxidative damage resulting fromuncontrolled metabolism occurring during the drying process.[4]See also • Micropropagation • Plant propagation • SeedbankNotes 1. ^ "Frequently Asked Questions". National Center for Genetic Resources Preservation, USDA. Retrieved on 2008-01-09. 2. ^ Berjak, Patricia; N.W. Pammenter; J. A. Vozzo Editor. "Ch 4. Orthodox and Recalcitrant Seeds" (PDF). Tropical Tree Seed Manual. USDA Forest Service. Retrieved on 2008-01-15. 3. ^ Connor, Kristina F (2004). "Update on oak seed quality research: Hardwood recalcitrant seeds". Proc. RMRS P (33): 111–116. USDA, Rocky Mountain Research Station. Retrieved on 2008-01-09. 4. ^ Leprince, Olivier; J Buitink and F Hoekstra (1999). "Axes and cotyledons of recalcitrant seeds of Castanea sativa Mill. exhibit contrasting responses of respiration to drying in relation to desiccation sensitivity". J. Exp. Bot. 50: 1515–1524. Oxford University Press. Retrieved on 2008-01-09.Seed companySeed companies produce and sell seeds for flowers, fruit and vegetables to the amateurgardener. The production of seed is a multi billion dollar business, which uses growingfacilities and growing locations world wide. While most seed is produced by largespecialist growers, large amounts are produced by small growers that produce only one toa few crop types. These larger companies supply seed both to commercial resellers andwholesalers. The resellers and wholesalers sell to vegetable and fruit growers, and tocompanies who package seed into packets and sell them on to the amateur gardener.Each seed company or reseller that sells retail, produces a catalogue – generallypublished during early winter for seed to be sown the following spring. These cataloguesare eagerly awaited by the amateur gardener, as during winter months there is little thatcan be done in the garden, so this time can be spent planning the following year’sgardening. Most companies run a mail order catalogue business, some also supply theirrange of seeds to garden centers and other retailers.Seed companies produce a huge range of seeds from highly developed F1 hybrids to openpollinated wild species. Many gardeners like to stick to old familiar varieties but eachyear seed companies produce new varieties for gardeners to try. They have extensiveresearch facilities to produce plants with better genetic materials that result in improveduniformity and gardening appeal. These improved qualities might include diseasePlant anatomy, From Wikipedia, the free encyclopedia 158
  • 159. resistance, higher yields, dwarf habit and vibrant or new colors. These improvements areoften closely guarded to protect them from being utilized by other producers, thus plantcultivars are often sold under their own names and by international laws protected frombeing grown for seed production by others. Along with the growth in the allotmentmovement, and the increasing popularity of gardening, there have emerged many smallindependent seed companies. Many of these are active in seed conservation andencouraging diversity. They often offer organic and open pollinated varieties of seeds asopposed to hybrids. Many of these varieties are heirloom varieties. The use of oldvarieties will continue to maintain diversity in the horticultural gene pool. There is a goodcase for amateur gardeners to use older (heirloom) varieties as the modern seed types areoften the same as those grown by commercial producers, and so characteristics which areuseful to them (e.g. vegetables ripening at the same time) may be unsuited to homegrowing.Seed packets and seed information A farmers son holding out seeds Generally, seed packets labels includes: • Common plant name and the botanical name (in parentheses). • Space and deep: how deep to place the seeds in the soil, space between plants (from one row to the other one and from one plant to the other one in the same row). • Height: approximate height the plant will reach when mature. • Soil: type of soil the plant prefers. • Water: It can indicate "keep the soil lightly damp", "bottom water the plant", "drench the soil with water", "daily misting of water" and "almost dry out before re-watering". • Sun: full direct sunlight, partial sun, diffused sunlight, or grows well in the shade. • Door: if the plant is best suited for growing Indoor, Outdoor or Both. • Live: Perennial or annual. • Planting, germination and harvest period: This information can be indicated by months or quarters of the year. • Special requirements, if necessary.This information can be represented graphically.See also • Seed bank • Arboretum • Biodiversity • MonocultureSeed orchardA seed orchard is an intensively-managed plantation of specifically-arranged treesaimed for mass production of genetically improved seeds to create plants, or directseeding for the establishment of new forest.Plant anatomy, From Wikipedia, the free encyclopedia 159
  • 160. Contents • 1 General • 2 Material and connection with breeding population • 3 Genetic diversity of seed orchard crops • 4 Management and practical examples • 5 Recent Seed orchard Research • 6 ReferencesGeneralSeed orchards are common method of mass-multiplication for transferring geneticallyimproved material from breeding population to production population (forests) and in thissense are often referred to as "multiplication" populations. A seed orchard is oftencomposed of grafts (vegetative copies) of selected genotypes, but seedling seed orchardsalso occur mainly to combine orchard with progeny testing. Seed orchards are the stronglink between breeding programs and plantation establishment. They are designed andmanaged to produce seeds of superior genetic quality compared to those obtained fromseed production areas, seed stands or unimproved stands.Material and connection with breeding populationIn first generation seeds orchards, the parents usually are phenotypically-selected trees. Inadvanced generation seed orchards, the seed orchards are harvesting the benefitsgenerated by tree breeding and the parents may be selected among the tested clones orfamilies. It is efficient to synchronise the productive live cycle of the seed orchards withthe cycle time of the breeding population. In the seed orchard, the trees can be arrangedin a design to keep the related individuals or cloned copies apart from each other. Seedorchards are the delivery vehicle for genetic improvement programs where trad-offgenetic gain and diversity is most important concern. Genetic gain of seed orchard cropsis depending primarily on the genetic superiority of the orchard parents, the gameticcontribution to the resultant seed crops and pollen contamination from outside seedorchards.Genetic diversity of seed orchard cropsSeed production and gene diversity is an important aspect when using improved materialslike seed orchard crops. Seed orchards crops derives generally from a limited number oftrees. But if it is a common wind-pollinated species much pollen will come from outsidethe seed orchard and widen the genetic diversity. The genetic gain of the first generationseed orchards is not so high and the seed orchard progenies overlaps with unimprovedmaterial. Gene diversity of the seed crops is greatly influenced by the relatedness(kinship) among orchard parents, the parental fertility variation and the pollencontamination.Management and practical examplesSeed orchards are usually managed to obtain sustainable and large crops of seeds of goodquality. To achieve this, the following means are commonly applied: orchards establishedon flat surface sites with southern exposition (better conditions for orchard maintenanceand for seed production), no stands of the same species in affinity (avoid strong pollencontamination), sufficient area to produce and be mainly pollinated with own pollencloud, cleaning the corridors between the rows, fertilising, and supplemental pollination.The genetic quality of seed orchards can be improved by genetic thinning and/or selectivePlant anatomy, From Wikipedia, the free encyclopedia 160
  • 161. harvesting [1]. In plantation forestry with southern pines in the United States, almost allplants originate from seed orchards and most plantations are planted in family blocks,thus the harvest from each clone is kept separate during seed processing, plant productionand plantation[2]. A recent conference proceedings about seed orchards is available on thenet [1].Recent Seed orchard Research • The optimal balance between effective number of clones (diversity, status number, gene diversity) and genetic gain is achieved by making clonal contributions (number of ramets) proportional (linearly dependent) to the genetic value ("linear deployment"). This is dependent on several assumptions, one of them that the contribution to the seed orchard crop is proportional to the number of ramets. But the more ramets the larger share of the pollen is lost depending on ineffective self-pollination. But even considering this, the linear deployment is a very good approximation[3]. It was thought that increasing the gain is always accompanied by a loss in effective number of clones, but it has shown that both desiderata can be obtained in the same time by genetic thinning using the linear deployment algorithm if applied to some rather unbalanced seed orchards.[4]. • The clonal variation in expected seed set has been compiled for 12 adult clonal seed orchards of Scots pine[5]. The seed set ability is not that drastic among clones as has been shown in other investigations which are probably less relevant for actual seed production of Scots pine. • The correlations of cone set for Scots pine in a clonal archieve was not well correlated with that of the same clones in seed orchards[6]. Thus it does not seem meaningful to increase seed set by choosing clones with a good seed set. • As supporting tree breeding make advances, new seed orchards will be genetically better than old ones. This is a relevant factor for the economic life-time of a seed orchard. Considerations for Swedish Scots pine suggested an economical life time 30 years, which is less than the current,[7]. • Seed orchards for important windpollinated species start to produce seeds before the seed orchard trees start to produce much pollen. Thus all or most of the pollen parents are outside the seed orchard. Calculations indicates that seed orchard seeds are still to be expected to a superior alternative to older and more mature seed orchards or stand seeds. Advantage of early seeds like absence of selfing or related matings and high diversity are positive factors in the early seeds [8]. • Swedish conifers orchards with tested clones could have 20-25 clones with more ramets from the better and less from the worse so effective ramet number is 15- 18. Higher clone number results in unneeded loss of genetic gain. Lower clone numbers can still be better than existing alternatives. For southern pines in United states it may be optimal with half as many clones.[9].References Kang, K.S. (2001) Genetic gain and gene diversity of seed orchard crops. Acta UniversitatisAgriculturae Sueciae, Silvestria 187. 75pp. Kang, K.S. and El-Kassaby, Y.A. 2002. Considerations of correlated fertility between genders ongenetic diversity: Pinus densiflora seed orchard as a model. Theor. Appl. Genet. (TAG) 105(8):1183-1189.Plant anatomy, From Wikipedia, the free encyclopedia 161
  • 162. Kang, K.S., Lindgren, D. and Mullin, T.J. 2004. Fertility variation, genetic relatedness and theireffects on gene diversity of seeds from a seed orchard of Pinus thunbergii. Silvae Genet. 53(5-6):202-206. Kang, K.S., El-Kassaby, Y.A., Han, S.U. and Kim, C.S. 2005. Genetic gain and diversity underdifferent thinning scenarios in a breeding seed orchard of Quercus acutissima. For. Ecol. &Manage. 212: 405-410. Kang, K.S. and Mullin T.J. 2007. Variation in clonal fertility and its effect on the gene diversityof seeds from a seed orchard of Chamaecyparis obtusa in Korea. Silvae Genet. 56(3-4): 134-137. 1. ^ Kang KS (2001) Genetic gain and gene diversity of seed orchard crops. Acta Universitatis Agriculturae Sueciae, Silvestria 187. 75pp. 2. ^ McKeand, S., T. Mullin, T. Byram and T. White. 2003. Deployment of genetically improved loblolly and slash pine in the South. J. For. 101(3): 32-37 3. ^ Prescher F, Lindgren D and El-Kassaby Y 2006. "Is linear deployment of clones optimal under different clonal outcrossing contributions in seed orchards?" Tree Genetics and Genomes 2:25-29. 4. ^ Prescher F, Lindgren D and Karlsson B 2008. Genetic Thinning of Clonal Seed Orchards using Linear deployment may improve both gain and diversity. Forest Ecology and Management 254: 188-192 5. ^ Prescher F, Lindgren D, Almqvist C, Kroon J, Lestander TA and Mullin TJ 2007. Variation in female fertility in mature Pinus sylvestris clonal seed orchards. Scandinavian Journal of Forest Research, 22:280-289 6. ^ Lindgren D, Tellalov Y and Prescher F 2007. Seed set for Scots pine grafts is difficult to predict In Proceedings of the IUFRO Division 2 Joint Conference: Low Input Breeding and Conservation of Forest Genetic Resources: Antalya, Turkey, 9-13 October 2006. Edited by Fikret Isik. p 139-141. 7. ^ El-Kassaby YA, Prescher F and Lindgren D 2007. Advanced generation seed orchards’ turnover as affected by breeding advance, time to sexual maturity, and costs, with special reference to Pinus sylvestris in Sweden. Scandinavian Journal of Forest Research 22:88- 98 8. ^ Nilsson J-E & Lindgren D 2005. Using seed orchard seeds with unknown fathers. In Fedorkov A (editor) Status, monitoring and targets for breeding programs. Proceedings of the meeting of Nordic forest tree breeders and forest geneticists, Syktyvkar 2005, ISBN 5-89606-249-4: 57-64. 9. ^ Lindgren D and Prescher F 2005. Optimal clone number for seed orchards with tested clones. Silvae Genetica 54: 80-92.Seed predation It has been suggested that this article or section be merged into Granivore. (Discuss)Seed predation includes any process inflicted on a plant’s seeds by an animal that resultsin the inviability of the seed. Generally this refers to the consumption and digestion of theseed, but also includes the parasitization of seeds by insect larvae (Janzen 1971). Thehigh nutrient content of seeds makes them a valuable food source for many mammals,birds and insects. Seed predation is an important ecological process that can affect thereproductive success of individual plants, the dynamics of plant populations (Crawley1992), and the evolution of defensive dispersal mechanisms and plant morphologicaltraits (Schöning et al. 2004).Seed predation may occur while seeds are still attached to the parent plant, or after theyhave been dispersed (Janzen 1971). General differences exist between pre- and post-Plant anatomy, From Wikipedia, the free encyclopedia 162
  • 163. dispersal seed predation in aspects such as the type of predator attending the seed(Crawley 1992) and the response of the plant to predation.Contents • 1 Pre-dispersal seed predation • 2 Post-dispersal seed predation • 3 Chemical defence of seeds • 4 Dispersal by seed predators • 5 See also • 6 ReferencesPre-dispersal seed predation Strawberry fruit damaged by a mouse eating the seeds Before dispersal, seeds are clustered in space and time, occurring in localised areas (i.e. on the plant) for relatively short periods of time (Crawley 1992). Additionally the presence of seeds on a plant may be advertised, intentionally or unintentionally, by the presence of flowers or fruits. Animals preying on undispersed seeds are typically small insects, such as flies, beetles, and mothlarvae, with limited mobility (Crawley 1992). These predators are often specialist feeders,restricted to one or a few plant species. However, larger generalist species, such as birdsand mammals, may also eat undispersed seed (Harper 1977).In response to pre-dispersal seed predation, plants may produce far more flowers thanthey are capable of supporting to full fruit maturity. This enables them to selectivelyabort damaged fruits and seeds, to prevent the input of further resources towards seedsthat will be unsuccessful (Crawley 1992).Post-dispersal seed predationOnce seeds have been dispersed they present a very different resource to potentialpredators. Dispersed seeds occur at low density and are sparsely distributed, and may bevery inconspicuous in the environment (Crawley 1992). Locating dispersed seeds is thusa very different process to locating undispersed seeds. Post-dispersal seed predators areusually larger and more mobile than pre-dispersal seed predators, and tend to begeneralists, able to use most of the seed they encounter (Crawley 1992). Rodents, birds,and ants are all important post-dispersal seed predators.Mast seeding may enable plants to avoid post-dispersal seed predation. This is whereplants in a population all produce their seeds at the same time, and the timing of suchseed production events varies between years, making it difficult for predators to predict(Kon et al. 2005). Mast seeding results in so much seed being produced at once thatpredators are unable to use all of it, so the remaining seed survives. Additionally, theperiods of time when no seed is being produced may reduce predator population sizes dueto the reduction in food available (Crawley 1992). The Japanese beech tree, Faguscrenata, is an example of a mast seeding species. In years when mast seeding does notoccur, there is a high rate of seed predation (about 80% of seeds are damaged) butpopulations of seed predators are kept small by the reduced availability of food. In yearswhere populations of Japanese beech produce 20 times more seed than in the previousPlant anatomy, From Wikipedia, the free encyclopedia 163
  • 164. season (i.e. mast seeding years), the reduced population of seed predators has a muchsmaller impact (about 30% of seeds are damaged) on the increased number of seedsproduced (Kon et al. 2005).Chemical defence of seedsA common plant defence strategy is the production of chemical compounds toxic toherbivores (Janzen 1971). A wide variety of defensive compounds are used, and thesemay be present in any part of a plant. Plants may use the same compound in differentstructures, such as leaves and seeds. However, predators of leaves are likely to differfrom seed predators, so different defensive compounds, specific to each type of predator,may be used in each type of structure (Janzen 1971). A chemical defence strategy mayprotect seeds both pre- and post-dispersal. The presence of toxic quinolizidine alkaloidsin the seeds of Ormosia arborea did not prevent their being collected and hoarded by red-rumped agoutis (Dasyprocta leporina), but they were not eaten after hoarding due to theirtoxic content (Guimaraes Jr. et al. 2003). In this example, the plant achieves dispersal ofits seeds by a potential predator.Dispersal by seed predatorsMany seed predators, particularly ants, birds and rodents, collect and store seed for laterconsumption (Harper 1977). If stores are surplus to the requirements of the predator,some of this seed may escape being eaten and be able to germinate. This will also dependon the type of store a seed finds itself in, as the stores of some predators are completelyunsuitable for seed germination. For example the acorn woodpecker stores acorns inindividual holes drilled in the trunks of trees (Harper 1977). However, seeds that areburied may have quite a good chance of germination, and may also enjoy benefits ofdispersal, through being transported away from the parent plant by the predator (Harper1977). Some plant species rely on seed predators for seed dispersal, and pay the cost of acertain level of seed mortality for the benefits gained through dispersal of just a few seeds(Crawley 1992).See also • GranivoreReferences • Crawley, M.J. 1992. Seed Predators and Population Dynamics. In: Seeds: The Ecology of Regeneration in Plant Communities. Fenner, M. (ed.). C.A.B. International, Oxon, U.K. • Guimaraes Jr., P.R., Jose, J., Galetti, M. and Trigo, J.R. 2003. Quinolizidine alkaloids in Ormosia arborea seeds inhibit predation but not hoarding by agoutis (Dasyprocta leporina). Journal of Chemical Ecology 29: 1065-1072 • Harper, J.L. 1977. Population Biology of Plants. Academic Press, New York, N.Y. • Janzen, D.H. 1971. Seed Predation by Animals. Annual Review of Ecology and Systematics 2: 465-492. • Kon, H., Noda, T., Terazawa, K., Koyama, H. and Yasaka, M. 2005. Evolutionary Advantages of Mast Seeding in Fagus crenata. Journal of Ecology 93: 1148- 1155. • Schöning, C., Espadaler, X., Hensen, I. and Roces, F. 2004. Seed Predation of the Tussock-grass Stipa tenacissima L. by Ants (Messor spp.) in South-eastern Spain: the Adaptive Value of Trypanocarpy. Journal of Arid Environments 56: 43-61.Plant anatomy, From Wikipedia, the free encyclopedia 164
  • 165. SeedbedFor the performance art piece, see Seedbed (performance piece).A seedbed or seedling bed is a specially prepared box used to grow plants in a controlledenvironment before transplanting them into a garden. A seedling bed is used to increasethe number of seeds that germinate. Once the seedlings have matured in the seedling bed,they are then transplanted into a larger bed or a garden.The preparation of a seedbed may include: 1. The removal of debris. Insect eggs and disease spores are often found in plant debris and so this is removed from the plot. Stones and larger debris will also physically prevent the seedlings from growing. 2. Levelling. The site will have been levelled for even drainage. 3. Breaking up the soil. Compacted soil will be broken up by digging. This allows air and water to enter, and helps the seedling penetrate the soil. Smaller seeds require a finer soil structure. The surface the soil can be broken down into a fine granular structure using a tool such as a rake. 4. Soil improvement. The soil structure may be improved by the introduction of organic matter such as compost or peat. 5. Fertilizing. The nitrate and phosphate levels of the soil can be adjusted with fertilizer. If the soil is deficient in any micro nutrients, these too can be added.The seedlings may be left to grow to adult plants in the seedbed, perhaps after thinning toremove the weaker ones, or they may be moved to a border as young plants.See also • Category:Gardening • Open field • Seed drill • False seedbed • Sowing • Stale seed bed • Stratification (botany)SeedlingFor other uses, see Seedling (disambiguation).Monocot (left) and dicot (right) seedlingsA seedling is a young plant sporophyte developing out of a plantembryo from a seed. Seedling development starts withgermination of the seed. A typical young seedling consists ofthree main parts: the radicle (embryonic root), the hypocotyl(embryonic shoot), and the cotyledons (seed leaves). The twoclasses of flowering plants are distinguished by their numbers ofseed leaves: Monocotyledons (monocots) have one blade-shapedcotyledon, whereas dicotyledons (dicots) have two roundcotyledons. Gymnosperms are more varied. For example, pineseedlings have up to eight cotyledons. The seedlings of someflowering plants have no cotyledons at all. These are said to beacotyledons.Plant anatomy, From Wikipedia, the free encyclopedia 165
  • 166. Contents • 1 Germination and early seedling development • 2 Photomorphogenesis and skotomorphogenesis • 3 Seedling growth and maturation • 4 Consumption of seedlings • 5 BibliographyGermination and early seedling developmentDevelopment of an angiosperm (maple) seedling Main article: GerminationDuring germination, the young plant emerges from its protective seed coat with its radiclefirst, followed by the cotyledons. The radicle orients towards gravity, while the hypocotylorients away from gravity and elongates through cell expansion to push the cotyledonsout of the ground.Photomorphogenesis and skotomorphogenesis Main article: Photomorphogenesis Main article: EtiolationDicot seedlings grown in the light develop short hypocotyls and open cotyledonsexposing the epicotyl. This is also referred to as photomorphogenesis. In contrast,seedlings grown in the dark develop long hypocotyls and their cotyledons remain closedaround the epicotyl in an apical hook. This is referred to as skotomorphogenesis oretiolation. Etiolated seedlings are yellowish in color as chlorophyll synthesis andchloroplast development depend on light. They will open their cotyledons and turn greenwhen treated with light.In a natural situation, seedling development starts with skotomorphogenesis while theseedling is growing through the soil and attempting to reach the light as fast as possible.During this phase, the cotyledons are tightly closed and form the apical hook to protectthe shoot apical meristem from damage while pushing through the soil. In many plants,the seed coat still covers the cotyledons for extra protection.Upon breaking the surface and reaching the light, the seedlings developmental programis switched to photomorphogenesis. The cotyledons open upon contact with lightPlant anatomy, From Wikipedia, the free encyclopedia 166
  • 167. (splitting the seed coat open, if still present) and become green, forming the firstphotosynthetic organs of the young plant. Until this stage, the seedling lives off theenergy reserves stored in the seed. The opening of the cotyledons exposes the shootapical meristem and the plumule consisting of the first true leaves of the young plant.The seedlings sense light through the light receptors phytochrome (red and far-red light)and cryptochrome (blue light). Mutations in these photo receptors and their signaltransduction components lead to seedling development that is at odds with lightconditions, for example seedlings that show photomorphogenesis when grown in thedark.Seedling growth and maturationDevelopment of a gymnosperm (Douglas fir) seedlingOnce the seedling starts to photosynthesize, it is no longer dependent on the seeds energyreserves. The apical meristems start growing and give rise to the root and shoot. The first"true" leaves expand and can often be distinguished from the round cotyledons throughtheir species-dependent distinct shapes. While the plant is growing and developingadditional leaves, the cotyledons eventually senesce and fall off.Consumption of seedlings This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (March 2007)Seedlings are commonly eaten as a health food. These seedlings are usually labeledsprouts, but in a botanical sense are actually seedlings. There is controversy in whetherseedlings, or sprouts, are really worth eating. These seedlings are used many times inorganic foods and are eaten for their concentrations of certain vitamins the seedlingnaturally contains. This can be viewed out of proportion as the seedling is usually toosmall to contain enough vitamins or minerals to be in line with the amount they areclaimed to obtain.BibliographyWikibooks has more on the topic ofSeedlingPlant anatomy, From Wikipedia, the free encyclopedia 167
  • 168. • P.H. Raven, R.F. Evert, S.E. Eichhorn (2005): Biology of Plants, 7th Edition, W.H. Freeman and Company Publishers, New York, ISBN 0-7167-1007-2 Wikimedia Commons has media related to: SeedlingsA seedling emerges Three-day-old sunflowerSeven-day-old pine seedlings seedlingStratification (botany)In horticulture, stratification is the process of pretreating seeds to simulate naturalconditions that a seed must endure before germination. Many seed species have what iscalled an embryonic dormancy and generally speaking will not sprout until thisdormancy is broken.Contents • 1 Examples • 2 Sanitary measures • 3 Preparing a stratifying medium • 4 Sowing and seedlings • 5 ReferencesExamplesFor seeds of trees and shrubs from temperate climates, stratification involves soaking andchilling seeds prior to sowing. This simulates natural conditions where the seeds wouldremain through a winter on cold, wet ground. Seeds will usually germinate promptly anduniformly after stratification. Unstratified seeds may take up to two years to germinate, ifthey do so at all.In the wild, seed dormancy is usually overcome by the seed spending time in the groundthrough a winter period and having their hard seed coat softened up by frost andweathering action. By doing so the seed is undergoing a natural form of "coldstratification" or pretreatment. This cold moist period triggers the seeds embryo, itsgrowth and subsequent expansion eventually break through the softened seed coat in itssearch for sun and nutrients.In its most basic form, when the cold stratification process is controlled, the pretreatmentamounts to nothing more than subjecting the seeds to storage in a cool (ideally +1° to+3°C; not freezing) and moist environment for a period found to be sufficient for thespecies in question. This period of time may vary from one to three months.To accomplish this you merely place the seeds in a sealed plastic bag with moistenedvermiculite (or sand or even a moistened paper towel) and refrigerate it. Use three timesthe amount of vermiculite as seeds. It is important to only slightly dampen thePlant anatomy, From Wikipedia, the free encyclopedia 168
  • 169. vermiculite, as excessive moisture can cause the seeds to grow mouldy in the bag. Assuch, err on the side of drier rather than wetter. To give an idea, it should not be possibleto squeeze any dripping water out of the vermiculite.After undergoing the recommended period of cold stratification, the seeds are ready to beremoved and sown in the nursery bed for germination.Sanitary measuresMany sources recommend using peat a combination of peat and sand, or vermiculitewhen cold stratifying seeds.[1][2][3]. The medium must be sterile to prevent harm to theseed by pathogens including fungi.[4]Preparing a stratifying mediumThe seeds should be cleaned of any additional material (fruit pulp, leaf and seed-podfragments, cone scales, etc), but the shells of nuts should not be removed.Use of a fungicide to moisten your stratifying vermiculite will help prevent fungaldiseases. This should be used as stipulated by the fungicide manufacturer. (Note: aconvenient and safe fungicide is Chinosol. It is primarily a disinfectant, non-toxic, andcan be used in solution from 0.1% for prevention, to 0.5% for treating an existinginfection. It is often recommended for growing succulents from seed, which are generallyprone to mold, so it should work well also for any other seed germination. It is notusually sold as a pesticide, but is available from vintner suppliers, as it is used for winemaking in small quantities.)Different seeds should be placed in different bags rather than putting them all into onebag, and large quantities are also best split into several small bags. That way any fungaloutbreak will be restricted to only some seeds. If no fungicide is used, a close checkshould be kept on the seeds, removing any which show signs of mould or become softand with a decaying smell.If an outbreak of fungus occurs, remove the seeds and re-apply fungicide, then placethem in a new bag with new slightly moistened vermiculite. Always keep the bag sealed.The stratifying seeds should be checked on a regular basis for either fungus orgermination. If any seeds germinate while in the refrigerator, they should be removed andsown.Any seeds that are indicated as needing a period of warm stratification followed by coldstratification should be subjected to the same measures, but the seeds should additionallybe stratified in a warm area first, followed by the cold period in a refrigerator later. Warmstratification requires temperatures of 15-20°C. In many instances, warm stratificationfollowed by cold stratification requirements can also be met by planting the seeds insummer in a mulched bed for expected germination the following spring. Some seedsmay not germinate until the second spring.Soaking the seeds in cold water for 6-12 hours immediately before placing them in coldstratification can cut down on the amount of time needed for stratification, as the seedneeds to absorb some moisture to enable the chemical changes that take place instratification.The time taken to stratify seeds depends on species and conditions; in many cases twomonths is sufficient to break the seed dormancy. After undergoing the cool moisttreatment the seeds are ready to plant and will usually sprout in a few days to weeks.Plant anatomy, From Wikipedia, the free encyclopedia 169
  • 170. Sowing and seedlingsMost seedlings, whether grown in pots or beds, benefit from good air circulation whichdiscourages fungus growth and promotes sturdy stems. Potting and germinatingmedium/soil is not critical as long as the soil is light as well as lightly firmed down butnot heavily compacted. Sterilised potting soil will minimize problems with Botrytis orPythium fungal disease. These problems are much more likely to occur if air circulationis poor.Most seeds need only be planted at a depth equal to their own thickness in order togerminate. Seeds planted outdoors are best planted little deeper to avoid disturbancecaused by heavy rainfall. The soil should be slightly damp but never soaking wet, norallowed to dry out completely.References 1. ^ Dan, Meyer. "Growing Wisconsin Trees From Seed". University of Wisconsin College of Agricultural and Life Sciences. Retrieved on 2008-07-01. 2. ^ "Germination of Tree Seed". University of Iowa Extension. Retrieved on 2008-07-01. 3. ^ "Growing Milkweed". University of Minnesota Monarch Lab. 4. ^ Paal, T.. "Dependency of Lingonberry Seed Germinating Ability on Seed Age and Storage Method". International Society for Horticultural Science.Retrieved from "http://en.wikipedia.org/wiki/Stratification_(botany)"A website devoted entirely to seeds!WELCOME to my webpages about seeds - collecting seeds, storing seeds, sowing seeds,germinating seeds and exchanging seeds, with pictures of seeds, seedpods and seedlings.If youre looking for pictures of seeds, there are life-size photos of 700 seeds here, arrangedroughly in order of size. There are photos of nearly 700 seedlings, and germination informationfor around 1500 species. The Botany Section covers hundreds of botanical and gardening terms,with charts and photos to make everything clear. Whether youre a gardener, a student, or ateacher, I hope you can find something useful here. (If youre a teacher, this page has links tosome topics that might be useful for the National Curriculum Key Stages in Science.) If you want to collect your own seeds, but arent sure what the Seeds and seedpod looks like, or if you have seeds without a name, hopefully this section will help you identify them. Life-size pictures of 700 seeds Seed Pods in order of size and shape, and a Database with photos and descriptions of the seedpods. A light-hearted look at seed collecting, which will tell you all you need to collect, dry and store seeds from the plants in your garden. Also Seed includes answers to some Frequently Asked Questions to help Harvesting ensure your seeds are ripe, healthy and viable, and seed envelope templates, including some with flower outlines for children to colour in. General information about how, when and where to sow seeds by Seed several different methods. Explains the reasons you might want to use winter sowing, and suggests plants you can start this way. Sowing Information on stratification, scarification, and answers to more FAQs.Plant anatomy, From Wikipedia, the free encyclopedia 170
  • 171. A Seed Germination Database - A table showing the results of Germination sowing almost 2000 batches of seeds of around 1500 species, by several different methods, at different times of the year. Photos of nearly 700 seedlings with their Latin names, or sorted Seedling according to the shape of the first true leaves, with their Latin and common names, to make it easier to identify the plants that come up Images in your garden, or to show you what should come up from the seeds you sow. Includes some FAQs about seedlings. 100 pages with photos and descriptions of 50 favourite annuals and Plant 50 favourite perennial plants to grow from seed. Includes their Profiles botanical classification, and the photographs of seedpod, seeds and seedlings from the other sections, together with germination hints. All the plants covered in these pages, listed by botanical name or Plant common name, linked to the relevant page so you can go straight to the information you want. Also has a Search Box, in case you cant! Index Or use the common names index to check the botanical names of your plants. Some technical bits - gardening and botanical terms, parts of a A Bit of flower, development of a seed, meaning of Latin names, botanical Botany names for common plants, Plant Families, pests, weeds, temperature zones and more, with explanatory photos, charts and diagrams.I hope you find these pages helpful. Once again, here are all the sections on the site About G. Leubner Website Gerhard Leubner Lab University Freiburg, GermanHomeLogin/Download NewsSeed Structure Seed Evolution 1Plant Hormones Endosperm weakeningSeed Ecology Seed modelingLab Members PublicationsResearch Projects Seed DictionarySeed Evolution 2 Seed GerminationWater relations ß-1,3-GlucanasesContact FreiburgHyperlinksSeed Dormancy 1 Seed Dormancy 2Plant anatomy, From Wikipedia, the free encyclopedia 171
  • 172. After–ripening Seed Technology:Hyperlink: Tansley Review "Seed Dormancy and the Control of Germination" by Finch-Savage andLeubner-Metzger (2006) Hyperlink: Table "Arabidopsis hormone mutants" - Review on plant hormoneinteractions by Kucera et al. (2005) Hyperlink: Table "Seed dormancy classification (phylogeny, examples)" (2006) Hyperlink: 9th ISSS Conference on Seed Biology in Olztyn, Poland, July 2008 -http://www.seedbio2008.pl Hyperlink: "Samen im Tiefschlaf" - BIOPRO - Das Biotech/Life Sciences PortalBaden-Württemberg Citation of this website: Leubner G (actual year). The Seed Biology Place -http://www.seedbiology.deAccessory fruit strawberry: the seeds (achenes) are the real fruit. An accessory fruit, false fruit, spurious fruit, epigynous fruit, syconium or pseudocarp is a fruit where the fleshy part is derived not from the ovary but from some adjacent tissue. An example is the apple.[citation needed] Other examplesinclude cashews and figs.The term includes false berries (e.g. the strawberry). This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (July 2007) ypes of fruitsBerries · False berries · Hesperidia · Drupes · Pomes · Compound fruits · Multiple fruits ·Accessory fruit This botany article is a stub. You can help Wikipedia by expanding it.Fruit anatomy (Redirected from Pericarp) Longitudinal section of female flower of squash (courgette), showing ovary, ovules, pistil, and petals.Plant anatomy, From Wikipedia, the free encyclopedia 172
  • 173. A fruit in botany refers to a mature ovary. In fleshy fruits, the outer, often edible, layer isthe pericarp, which is the tissue that develops from the ovary wall of the flower andsurrounds the seeds. If seeds are considered to be akin to eggs eggs developing in theovary of a fowl, the pericarp would be the female birds uterus.However, there are a large number of fruits which are not adequately described by thatanalogy; for example in most nuts and legumes the edible part is the seed and not thepericarp. Many edible vegetables are actually stems, leaves, and even roots of the plant,but others like the cucumber, squash etc. are the common pericarp and are botanicallyconsidered to be fruits. Finally, in some seemingly pericarp fruits the edible portion isactually an aril.Contents • 1 Categories of fruits • 2 Anatomy of simple fruits o 2.1 Pericarp layers 2.1.1 Exocarp 2.1.2 Mesocarp 2.1.3 Endocarp o 2.2 Anatomy of grass fruits • 3 See also • 4 ReferencesCategories of fruitsFruits come in three main anatomical categories: • Simple fruits are formed from a single ovary and may contain one to many seeds. They can be either fleshy or dry. Examples of simple fleshy fruits are berries, drupes and pomes. Examples of dry fruits include nuts and grains. • Aggregate fruits are formed from a single compound flower and contain many ovaries. Examples include raspberries and blackberries. • Multiple fruits are formed from the fused ovaries of multiple flowers. An example for a multiple fruit is pineapple.Anatomy of simple fruitsDiagram of a typical drupe (peach), showing both fruit and seedIn berries and drupes, the pericarp forms the edible tissue around the seeds. In accessoryfruits, other tissues develop into the edible portion of the fruit instead, for example thereceptacle of the flower in apples and strawberries.Plant anatomy, From Wikipedia, the free encyclopedia 173
  • 174. Pericarp layersThe pericarp itself is typically made up of three distinct layers: the exocarp which is themost outside layer or peel, the mesocarp the middle layer or pith, and the endocarp theinner layer surrounding the hollowed ovary or the containing seeds.ExocarpExocarp (Gr. "outside" + "fruit"), is a botanical term for the outermost layer of thepericarp (or fruit). The exocarp forms the tough outer skin of the fruit which bears oilglands and pigments. The exocarp is sometimes called the epicarp, or, especially incitruses, the flavedo.A schematic picture of an orange hesperidiumFlavedo is mostly composed of cellulosic material but also contains other components,such essential oils, paraffin waxes, steroids and triterpenoids, fatty acids, pigments(carotenoids, chlorophylls, flavonoids), bitter principles (limonene), and enzymes.In citrus fruits, the flavedo constitutes the peripheral surface of the pericarp. It iscomposed of several cell layers that become progressively thicker in the internal part; theepidermic layer is covered with wax and contains few stomata, which in many cases areclosed when the fruit is ripe.When ripe, the flavedo cells contain carotenoids (mostly xanthophyll) insidechromoplasts which, in a previous developmental stage, contained chlorophyll. Thishormonally controlled progression in development is responsible for the fruits change ofcolor from green to yellow upon ripening.The internal region of the flavedo is rich in multicellular bodies with spherical orpyriform shapes, which are full of essential oils.MesocarpMesocarp (Gr. "middle" + "fruit") or Sarcocarp (Gr. "flesh" + "fruit"), is the botanicalterm for the succulent and fleshy middle layer of the pericarp of drupaceous fruit,between the exocarp and the endocarp; it is usually the part of the fruit that is eaten.This term may also refer to any fruit which is fleshy throughout. In a hesperidium, themesocarp is also referred to as albedo or pith because of its soft fiber. It is part of the peelwhich is commonly removed by hand.EndocarpPlant anatomy, From Wikipedia, the free encyclopedia 174
  • 175. Endocarp (Gr. "inside" + "fruit"), is a botanical term for the inside layer of the pericarp(or fruit), which directly surrounds the seeds. It may be membranous as in citrus where itis the only part consumed, or thick and hard as in the stone fruits of the subfamilyPrunoideae such as peaches, cherries, plums, and apricots.In nuts, it is the stony layer that surrounds the kernel of pecans, walnuts etc. and which isremoved prior to consumption.Anatomy of grass fruitsThe grains of grasses are single-seeded simple fruits where the pericarp (ovary wall) andseed coat are fused into one layer. This type of fruit is called a caryopsis. Examplesinclude cereal grains, such as wheat, barley and rice.See also Wikimedia Commons has media related to: Fruit anatomy • Peel (fruit) • Hesperidium the common citrus berry. BarkFor other uses, see Bark (disambiguation).Japanese Maple bark.Bark of a Pine tree in Tecpan, Guatemala.Bark, also known as periderm, is the outermost layer of stems and roots of woody plantssuch as trees. It overlays the wood and consists of three layers, the cork or phellem, thephelloderm and the cork cambium or phellogen. Products used by people that are derivedfrom bark include: spices and other flavorings, tannin, resin, latex, medicines, poisons,various hallucinatory chemicals and cork. Bark has been used to make cloths, canoes,ropes and used as a surface for paintings and map making;[1] A number of plants are alsogrown for their attractive or interesting bark colorations and surface textures.[2][3]Plant anatomy, From Wikipedia, the free encyclopedia 175
  • 176. Contents • 1 Botanic description • 2 Uses • 3 Bark removal • 4 Bark repair • 5 Gallery • 6 See also • 7 ReferencesBotanic description • Cork - an external, secondary tissue impermeable to water and gases. • Cork cambium - A layer of cells, normally one or two cell layers thick that is in a persistent meristematic state that produces cork. • Phelloderm - (not always present) A layer of cells formed in some plants from the inner cells of the cork cambium (Cork is produced from the outer layer). • Cortex - The primary tissue of stems and roots. In stems the cortex is between the epidermis layer and the phloem, in roots the inner layer is not phloem but the pericycle. • Phloem - nutrient-conducting tissue composed of sieve tube or sieve cells mixed with parenchyma and fibers.In old stems the epidermal layer, cortex, and primary phloem become separated from theinner tissues by thicker formations of cork. Due to the thickening cork layer these cellsdie because they do not receive water and nutrients. This dead layer is the rough corkybark that forms around tree trunks and other stems. In smaller stems and on typically nonwoody plants, sometimes a secondary covering forms called the periderm, which is madeup of cork cambian, cork and phelloderm. It replaces the dermal layer and acts as acovering much like the corky bark, it too is made up of mostly dead tissue. The skin onthe potato is a periderm.Definitions of the term can vary. In another usage, bark consists of the dead andprotective tissue found on the outside of a woody stem, and does not include the vasculartissue.The vascular cambium is the only part of a woody stem where cell division occurs. Itcontains undifferentiated cells that divide rapidly to produce secondary xylem to theinside and secondary phloem to the outside.Along with the xylem, the phloem is one of the two tissues inside a plant that areinvolved with fluid transport. The phloem transports organic molecules (particularlysugars) to wherever they are needed.UsesCork, sometimes confused with bark in colloquial speech, is the outermost layer of awoody stem, derived from the cork cambium. It serves as protection against damage,parasites and diseases, as well as dehydration and extreme temperatures. Cork cancontain antiseptics like tannins. Some cork is substantially thicker, providing furtherinsulation and giving the bark a characteristic structure, in some cases thick enough to beharvestable as cork product without killing the tree. Bark has been used a covering in themaking of canoes, the most famous example of this is the birch canoes of NorthAmerica.[4]The bark of some trees is edible.Plant anatomy, From Wikipedia, the free encyclopedia 176
  • 177. Among the commercial products made from bark are cork, cinnamon, quinine[5] (from thebark of Cinchona)[6] and aspirin (from the bark of willow trees). The bark of some treesnotably oak (Quercus robur) is a source of tannic acid, which is used in tanning. Barkchips generated as a by-product of lumber production, are often used in bark mulch inwestern North America. Bark is important to the horticultural industry since in shreddedform it is used for plants that do not thrive in ordinary soil, such as epiphytes.Wood Adhesives from Bark-Derived Phenols: Wood Bark has lignin content and when itis pyrolyzed (subjected to high temperatures in the absence of oxygen), it yields a liquidbio-oil product rich in natural phenol derivatives. The phenol derivatives are isolated andrecovered for application as a replacement for fossil-based phenols in phenol-formaldehyde (PF) resins used in Oriented Strand Board (OSB) and plywood.Bark removalCut logs used for the production of lumber or even log cabins generally have the barkremoved, either just before cutting or for curing. Such logs and even trunks and branchesfound in their natural state of decay in forests, where the bark has fallen off, are said to bedecorticated.A number of living organisms live in or on bark, including insects,[7] fungi and otherplants like mosses , algae and other vascular plants. Many of these organisms arepathogens or parasites but some also have symbiotic relationships.Bark repair Extensive callus growth on a young Ash tree. Alder bark (Alnus glutinosa) with characteristic lenticels and abnormal lenticels on callused areas.The degree to which trees are able to repair gross physical damage to their bark is veryvariable. Some are able to produce a callus growth which heals over the wound rapidly,but leaves a clear scar, whilst others such as oaks do not produce an extensive callusrepair.GalleryEucalypt bark Monterey PineA rare Black PoplarPlant anatomy, From Wikipedia, the free encyclopedia 177
  • 178. Acer capillipesbark tree, showing the (Red Snakebark bark and burrs. Maple) See also Wikimedia Commons has media related to: Bark • Bark painting • Bark beetleThe typical appearance of • Trunk (botany)Sycamore bark from an oldtree.References 1. ^ Taylor, Luke. 1996. Seeing the inside bark painting in western Arnhem Land. Oxford studies in social and cultural anthropology. Oxford: Clarendon Press. 2. ^ Sandved, Kjell Bloch, Ghillean T. Prance, and Anne E. Prance. 1993. Bark the formation, characteristics, and uses of bark around the world. Portland, Or: Timber Press. 3. ^ Vaucher, Hugues, and James E. Eckenwalder. 2003. Tree bark a color guide. Portland: Timber 4. ^ Adney, Tappan, and Howard Irving Chapelle. 1964. The bark canoes and skin boats of North America. Washington: Smithsonian Institution. 5. ^ Duran-Reynals, Marie Louise de Ayala. 1946. The fever bark tree; the pageant of quinine. Garden City, N.Y.: Doubleday. 6. ^ Markham, Clements R. 1880. Peruvian bark. A popular account of the introduction of chinchona cultivation into British India. London: J. Murray. 7. ^ Lieutier, François. 2004. Bark and wood boring insects in living trees in Europe a synthesis. Dordrecht: Kluwer Academic Publishers. Cork cambium (Redirected from Cork (tissue))Plant anatomy, From Wikipedia, the free encyclopedia 178
  • 179. Multiple cross sections of a stem showing cork cambium (click image 3 times to seedetail)[1]Cork cambium is a tissue found in many vascular plants as part of the periderm. Thecork cambium is a lateral meristem and is responsible for secondary growth that replacesthe epidermis in roots and stems. It is found in woody and many herbaceous dicots,gymnosperms and some monocots, which usually lack secondary growth.Cork cambium is one of the plants meristems - the series of tissues consisting ofembryonic (incompletely differentiated) cells from which the plant grows. It is one of themany layers of bark, between the cork and primary phloem. The function of corkcambium is to produce the cork, a tough protective material.Synonyms for cork cambium are bark cambium, pericambium or phellogen. Phellogenis defined as the meristematic cell layer responsible for the development of the periderm.Cells that grow inwards from the phellogen are termed phelloderm, and cells thatdevelops outwards are termed phellem or cork (note similarity with vascular cambium).The periderm thus consists of three different layers: • phelloderm, • phellogen (cork cambium) and • phellem.Growth and development of cork cambium is very variable between different species,and also highly dependent on age, growth conditions etc. as can be observed from thedifferent surfaces of bark; smooth, fissured, tesselated, scaly, flaking off, etc.Economic importance • Commercial cork is derived from the bark of the cork oak (Quercus suber). Cork has many uses including wine bottle stoppers, bulletin boards, coasters, hot pads to protect tables from hot pans, insulation, sealing for lids, flooring, gaskets for engines, fishing bobbers, handles for fishing rods and tennis rackets, etc. • Many types of bark are used as mulch.See also • Meristem • Cork (material) • Vascular cambiumReferences 1. ^ Winterborne J, 2005. Hydroponics - Indoor Horticulture [1] • Junikka, L. (1994) Macroscopic bark terminology. IAWA Journal 15(1): 3-45 • Trockenbrodt, M. (1990) Survey and discussion of the terminology used in bark anatomy. IAWA Bulletin, New Series 11: 141-166.Plant anatomy, From Wikipedia, the free encyclopedia 179
  • 180. Phloem Cross-section of a flax plant stem: 1. Pith, 2. Protoxylem, 3. Xylem I, 4. Phloem I, 5. Sclerenchyma (bast fibre), 6. Cortex, 7. Epidermis In vascular plants, phloem is the living tissue that carries organic nutrients (known as photosynthate), particularly sucrose, a sugar, toall parts of the plant where needed. In trees, the phloem is the innermost layer of the bark,hence the name, derived from the Greek word φλόος (phloos) "bark". The phloem ismainly concerned with the transport of soluble organic material made duringphotosynthesis. This is called translocation.Contents • 1 Structure o 1.1 Sieve tubes o 1.2 Companion cells • 2 Function o 2.1 Girdling • 3 Origin • 4 Nutritional use • 5 See also • 6 ReferencesStructureMultiple cross sections of a stem showing phloem and companion cells[1]Phloem tissue consists of less specialized and nucleate parenchymacells, sieve-tube cells, and companion cells (in addition albuminouscells, fibers and sclereids).Sieve tubesThe sieve-tube cells lack a nucleus, have very few vacuoles, butcontain other organelles such as ribosomes. The endoplasmicreticulum is concentrated at the lateral walls. Sieve-tube membersare joined end to end to form a tube that conducts food materialsthroughout the plant. The end walls of these cells have many smallpores and are called sieve plates and have enlarged plasmodesmata.Companion cellsThe survival of sieve-tube members depends on a close associationwith the companion cells. All of the cellular functions of a sieve-Plant anatomy, From Wikipedia, the free encyclopedia 180
  • 181. tube element are carried out by the (much smaller) companion cell, a typical plant cell,except the companion cell usually has a larger number of ribosomes and mitochondria.This is because the companion cell is more metabollically active than a typical plant cell.The cytoplasm of a companion cell is connected to the sieve-tube element byplasmodesmata.There are three types of companion cell. 1. Ordinary companions cells - which have smooth walls and few or no plasmodesmata connections to cells other than the sieve tube. 2. Transfer cells - which have much folded walls that are adjacent to non-sieve cells, allowing for larger areas of transfer. They are specialised in scavenging solutes from those in the cell walls which are actively pumped requiring energy. 3. Intermediary cells - which have smooth walls and numerous plasmodesmata connecting them to other cells.The first two types of cell collect solutes through apoplastic (cell wall) transfers, whilstthe third type can collect solutes symplastically through the plasmodesmata connections.FunctionUnlike xylem (which is composed primarily of dead cells), the phloem is composed ofstill-living cells that transport sap. The sap is a water-based solution, but rich in sugarsmade by the photosynthetic areas. These sugars are transported to non-photosyntheticparts of the plant, such as the roots, or into storage structures, such as tubers or bulbs.The Pressure flow hypothesis was a hypothesis proposed by Ernst Munch in 1930 thatexplained the mechanism of phloem translocation[2]. A high concentration of organicsubstance inside cells of the phloem at a source, such as a leaf, creates a diffusiongradient that draws water into the cells. Movement occurs by bulk flow; phloem sapmoves from sugar sources to sugar sinks by means of turgor pressure. A sugar source isany part of the plant that is producing or releasing sugar. During the plants growthperiod, usually during the spring, storage organs such as the roots are sugar sources, andthe plants many growing areas are sugar sinks. The movement in phloem is bidirectional,whereas, in xylem cells, it is unidirectional (upward).After the growth period, when the meristems are dormant, the leaves are sources, andstorage organs are sinks. Developing seed-bearing organs (such as fruit) are always sinks.Because of this multi-directional flow, coupled with the fact that sap cannot move withease between adjacent sieve-tubes, it is not unusual for sap in adjacent sieve-tubes to beflowing in opposite directions.While movement of water and minerals through the xylem is driven by negativepressures (tension) most of the time, movement through the phloem is driven by positivehydrostatic pressures. This process is termed translocation, and is accomplished by aprocess called phloem loading and unloading. Cells in a sugar source "load" a sieve-tubeelement by actively transporting solute molecules into it. This causes water to move intothe sieve-tube element by osmosis, creating pressure that pushes the sap down the tube.In sugar sinks, cells actively transport solutes out of the sieve-tube elements, producingthe exactly opposite effect.Some plants however appear not to load phloem by active transport. In these cases amechanism known as the polymer trap mechanism was proposed by Robert Turgeon[3]. Inthis case small sugars such as sucrose move into intermediary cells through narrowplasmodesmata, where they are polymerised to raffinose and other largerPlant anatomy, From Wikipedia, the free encyclopedia 181
  • 182. oligosaccharides. Now they are unable to move back, but can proceed through widerplasmodesmata into the sieve tube element.The symplastic phloem loading is confined mostly to plants in tropical rain forests and isseen as more primitive. The actively-transported apoplastic phloem loading is viewed asmore advanced, as it is found in the later-evolved plants, and particularly in those intemperate and arid conditions. This mechanism may therefore have allowed plants tocolonise the cooler locations.Organic molecules such as sugars, amino acids, certain hormones, and even messengerRNAs are transported in the phloem through sieve tube elements.Girdling Main article: GirdlingBecause phloem tubes sit on the outside of the xylem in most plants, a tree or other plantcan be effectively killed by stripping away the bark in a ring on the trunk or stem. Withthe phloem destroyed, nutrients cannot reach the roots and the tree/plant will die. Treeslocated in areas with animals such as beavers are vulnerable since beavers chew off thebark at a fairly precise height. This process is known as girdling, and can be used foragricultural purposes. For example, enormous fruits and vegetables seen at fairs andcarnivals are produced via girdling. A farmer would place a girdle at base of a largebranch, and remove all but one fruit/vegetable from that branch. Thus, all the sugarsmanufactured by leaves on that branch have no sinks to go to but the one fruit/vegetablewhich thus expands to many times normal size.OriginThe phloem originates, and grows outwards from, meristematic cells in the vascularcambium. Phloem is produced in phases. Primary phloem is laid down by the apicalmeristem. Secondary phloem is laid down by the vascular cambium to the inside of theestablished layer(s) of phloem.Nutritional usePhloem of pine trees has been used in Finland as a substitute food in times of famine, andeven in good years in the northeast, where supplies of phloem from earlier years helpedstave off starvation somewhat in the great famine of the 1860s. Phloem is dried andmilled to flour (pettu in Finnish) and mixed with rye to form a hard dark bread. Recently,pettu has again become available as a curiosity, and some have made claims of healthbenefits.See also • Xylem • Apical dominanceReferences 1. ^ Winterborne J, 2005. Hydroponics - Indoor Horticulture [1] 2. ^ Münch, E (1930). "Die Stoffbewegunen in der Pflanze". Verlag von Gustav Fischer, Jena: 234. 3. ^ Turgeon, R (1991). "Symplastic phloem loading and the sink-source transition in leaves: a model". VL Bonnemain, S Delrot, J Dainty, WJ Lucas, (eds) Recent Advances Phloem Transport and Assimilate Compartmentation.Plant anatomy, From Wikipedia, the free encyclopedia 182
  • 183. XylemMultiple cross sections of a flowering plant stem showing primary and secondary xylemand phloem[1]In vascular plants, xylem is one of the two types of transport tissue, phloem being theother. The word "xylem" is derived from classical Greek ξυλον (xylon), "wood", andPlant anatomy, From Wikipedia, the free encyclopedia 183
  • 184. indeed the best known xylem tissue is wood, though it is found throughout the plant. Itsbasic function is to transport water.Contents • 1 Physiology of xylem • 2 Anatomy of xylem • 3 Primary and secondary xylem • 4 Evolution of xylem • 5 See also • 6 References o 6.1 General referencesPhysiology of xylemThe xylem is responsible for the transport of water and soluble mineral nutrients from theroots throughout the plant. It is also used to replace water lost during transpiration andphotosynthesis. Xylem sap consists mainly of water and inorganic ions, although it cancontain a number of organic chemicals as well. This transport is not powered by energyspent by the tracheary elements themselves, which are dead at maturity and no longerhave living contents. Two phenomena cause xylem sap to flow: • Transpirational pull: the most important cause of xylem sap flow is the evaporation of water from the surfaces mesophyll cells to the atmosphere. This transpiration causes millions of minute menisci to form in the mesophyll cell wall. The resulting surface tension causes a negative pressure or tension in the xylem that pulls the water from the roots and soil. • Root pressure: If the water potential of the root cells is more negative than the soil, usually due to high concentrations of solute, water can move by osmosis into the root. This causes a positive pressure that forces sap up the xylem towards the leaves. In some circumstances the sap will be forced from the leaf through a hydathode in a phenomenon known as guttation. Root pressure is highest in the morning before the stomata open and allow transpiration to begin. Different plant species can have different root pressures even in a similar environment; examples include up to 145 kPa in Vitis riparia but around zero in Celastrus orbiculatus[2].Anatomy of xylemXylem can be found: • in vascular bundles, present in non-woody plants and non-woody plant parts • in secondary xylem, laid down by a meristem called the vascular cambium • as part of a stelar arrangement not divided into bundles, as in many ferns.Note that, in transitional stages of plants with secondary growth, the first two categoriesare not mutually exclusive, although usually a vascular bundle will contain primaryxylem only.The most distinctive cells found in xylem are the tracheary elements: tracheids and vesselelements. However, the xylem is a complex tissue of plants, which means that it includesmore than one type of cell. In fact, xylem contains other kinds of cells, such asparenchyma, in addition to those that serve to transport water.Plant anatomy, From Wikipedia, the free encyclopedia 184
  • 185. Primary and secondary xylemPrimary xylem is the xylem that is formed during primary growth from procambium. Itincludes protoxylem and metaxylem. Metaxylem develops after the protoxylem butbefore secondary xylem. It is distinguished by wider vessels and tracheids.Secondary xylem is the xylem that is formed during secondary growth from vascularcambium. Although secondary xylem is also found in members of the "gymnosperm"groups Gnetophyta and Ginkgophyta and to a lesser extent in members of theCycadophyta, the two main groups in which secondary xylem can be found are: 1. conifers (Coniferae): there are some six hundred species of conifers. All species have secondary xylem, which is relatively uniform in structure throughout this group. Many conifers become tall trees: the secondary xylem of such trees is marketed as softwood. 2. angiosperms (Angiospermae): there are some quarter of a million to four hundred thousand species of angiosperms. Within this group secondary xylem has not been found in the monocots. In the remainder of the angiosperms this secondary xylem may or may not be present, this may vary even within a species, depending on growing circumstances. In view of the size of this group it will be no surprise that no absolutes apply to the structure of secondary xylem within the angiosperms. Many non-monocot angiosperms become trees, and the secondary xylem of these is marketed as hardwood.Evolution of xylemPhotos showing xylem elements in the shoot of a fig tree (Ficus alba): crushed inhydrochloric acid, between slides and cover slips.Xylem appeared early in the history of terrestrial plant life. Fossil plants withanatomically preserved xylem are known from the Silurian (more than 400 million yearsago), and trace fossils resembling individual xylem cells may be found in earlierOrdovician rocks. The earliest true and recognizable xylem consists of tracheids with ahelical-annular reinforcing layer added to the cell wall. This is the only type of xylemfound in the earliest vascular plants, and this type of cell continues to be found in theprotoxylem (first-formed xylem) of all living groups of plants. Several groups of plantslater developed pitted tracheid cells, apparently through convergent evolution. In livingplants, pitted tracheids do not appear in development until the maturation of themetaxylem (following the protoxylem).In most plants, pitted tracheids function as the primary transport cells. The other type oftracheary element, besides the tracheid, is the vessel element. Vessel elements are joinedby perforations into vessels. In vessels, water travels by bulk flow, like in a pipe, ratherPlant anatomy, From Wikipedia, the free encyclopedia 185
  • 186. than by diffusion through cell membranes. The presence of vessels in xylem has beenconsidered to be one of the key innovations that led to the success of the angiosperms[3].However, the occurrence of vessel elements is not restricted to angiosperms, and they areabsent in some archaic or "basal" lineages of the angiosperms: (e.g., Amborellaceae,Tetracentraceae, Trochodendraceae, and Winteraceae), and their secondary xylem isdescribed by Arthur Cronquist as "primitively vesselless". Cronquist considered thevessels of Gnetum to be convergent with those of angiosperms[4]. Whether the absence ofvessels in basal angiosperms is a primitive condition is contested, the alternativehypothesis being that vessel elements originated in a precursor to the angiosperms andwere subsequently lost.See also • Cohesion-tension theory • Phloem • Secondary growth • Transpirational pull • Vascular tissue • Vascular bundleReferences 1. ^ Winterborne J, 2005. Hydroponics - Indoor Horticulture [1] 2. ^ Tim J. Tibbetts; Frank W. Ewers (2000). "Root pressure and specific conductivity in temperate lianas: exotic Celastrus orbiculatus (Celastraceae) vs. native Vitis riparia (Vitaceae)". American Journal of Botany 87: 1272–78. doi:10.2307/2656720. PMID 10991898. 3. ^ Carlquist, S.; E.L. Schneider (2002). "The tracheid–vessel element transition in angiosperms involves multiple independent features: cladistic consequences". American Journal of Botany 89: 185–195. doi:10.3732/ajb.89.2.185. 4. ^ Cronquist, A. (Aug 1988.). The Evolution and Classification of Flowering Plants. New York, New York: New York Botanical Garden Press. ISBN 978-0893273323.General references • Campbell, Neil A.; Jane B. Reece (2002). Biology, 6th ed., Benjamin Cummings. ISBN 978-0805366242. • Kenrick, Paul; Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D. C.: Smithsonian Institution Press. ISBN 1-56098-730-8. • Muhammad, A.F.; R. Sattler (1982). "Vessel Structure of Gnetum and the Origin of Angiosperms". American Journal of Botany 69 (6): 1004–21. doi:10.2307/2442898. • Melvin T. Tyree; Martin H. Zimmermann (2003). Xylem Structure and the Ascent of Sap, 2nd ed., Springer. ISBN 3-540-43354-6. recent update of the classic book on xylem transport by the late Martin ZimmermannVascular cambiumPlant anatomy, From Wikipedia, the free encyclopedia 186
  • 187. Multiple cross sections of a stem showing vascular cambium and companion cells[1] The vascular cambium is a lateral meristem in the vascular tissue of plants. The vascular cambium is the source of both the secondary xylem (inwards, towards the pith) and the secondary phloem (outwards), and is located between these tissues in the stem and root. A few leaves even have a vascular cambium.[2] The vascular cambium usually consist of two types of cells: • Fusiform initials (tall cells, axially-oriented) • Ray initials (almost isodiametric cells - smaller and round to angular in shape) Vascular cambium is a type of meristem - a tissue consisting of embryonic (incompletely differentiated) cells from which other (and more differentiated) plant tissues originate. Primary meristems are the apical meristems on root tips and shoot tips. Another lateral meristem is the cork cambium, which produces cork, part of the bark. Vascular cambia are found in dicots and gymnosperms but not monocots, which usually lacksecondary growth.For successful grafting, the vascular cambia of the stock and scion must be aligned sothey can grow together.Synonyms • Wood cambium • Main cambium • Bifacial cambiumPlant anatomy, From Wikipedia, the free encyclopedia 187
  • 188. References 1. ^ Winterborne J, 2005. Hydroponics - Indoor Horticulture [1] 2. ^ Ewers, F.W. 1982. Secondary growth in needle leaves of Pinus longaeva (bristlecone pine) and other conifers: Quantitative data. American Journal of Botany 69: 1552-1559. [2]See also • Meristem • Cork cambium • Unifacial cambiumExternal links • Pictures of Vascular cambium • Detailed description - James D. MausethWood It has been suggested that Sapwood be merged into this article or section. (Discuss)For other uses, see Wood (disambiguation)."Wooden" redirects here. For other uses, see Wooden (disambiguation).Wood is hard, fibrous, lignified structural tissue produced as secondary xylem in thestems of woody plants, notably trees but also shrubs. In a living tree it conducts water andnutrients to the leaves and other growing tissues, and has a support function, enablingplants to reach large sizes. Wood may also refer to other plant materials and tissues withcomparable properties.Artists can use wood to create delicate sculptures.People have used wood for millennia for many purposes, primarily as a constructionmaterial, for making tools, weapons, furniture and artworks and as a fuel. Wood can bedated to make inferences about when a wooden object was created and the climate at thattime.Plant anatomy, From Wikipedia, the free encyclopedia 188
  • 189. Contents • 1 Formation o 1.1 Knots o 1.2 Heartwood and sapwood • 2 Different woods o 2.1 Colour o 2.2 Structure o 2.3 Monocot wood • 3 Water content • 4 Uses o 4.1 Fuel o 4.2 Construction • 5 See also • 6 Notes • 7 ReferencesFormationA tree increases in diameter by the formation, between the old wood and the inner bark,of new woody layers which envelop the entire stem, living branches, and roots. Wherethere are clear seasons, this can happen in a discrete pattern, leading to what is known asgrowth rings, as can be seen on the end of a log. If these seasons are annual these growthrings are annual rings. Where there is no seasonal difference growth rings are likely to beindistinct or absent.Within a growth ring it may be possible to see two parts. The part nearest the center ofthe tree is more open textured and almost invariably lighter in colour than that near theouter portion of the ring. The inner portion is formed early in the season, when growth iscomparatively rapid; it is known as early wood or spring wood. The outer portion is thelate wood or summer wood, being produced in the summer.[1] In white pines there is notmuch contrast in the different parts of the ring, and as a result the wood is very uniformin texture and is easy to work. In hard pines, on the other hand, the late wood is verydense and is deep-colored, presenting a very decided contrast to the soft, straw-coloredearly wood. In ring-porous woods each seasons growth is always well defined, becausethe large pores of the spring abut on the denser tissue of the fall before. In the diffuse-porous woods, the demarcation between rings is not always so clear and in some cases isalmost (if not entirely) invisible to the unaided eye.KnotsPlant anatomy, From Wikipedia, the free encyclopedia 189
  • 190. A knot on a tree at the Garden of the Gods public park in Colorado Springs, Colorado(October 2006).A knot is a particular type of imperfection in a piece of timber, which reduces itsstrength, but which may be exploited for artistic effect. In a longitudinally-sawn plank, aknot will appear as a roughly circular "solid" (usually darker) piece of wood aroundwhich the roughly parallel fibres (grain) of the rest of the "flows" (parts and rejoins).A knot is actually a portion of a side branch (or a dormant bud) included in the wood ofthe stem or larger branch. The included portion is irregularly conical in shape (hence theroughly circular cross-section) with the tip at the point in stem diameter at which theplants cambium was located when the branch formed as a bud. Within a knot, the fibredirection (grain) is up to 90 degrees different from the fibres of the stem, thus producinglocal cross grain.During the development of a tree, the lower limbs often die, but may persist for a time,sometimes years. Subsequent layers of growth of the attaching stem are no longerintimately joined with the dead limb, but are grown around it. Hence, dead branchesproduce knots which are not attached, and likely to drop out after the tree has been sawninto boards.In grading lumber and structural timber, knots are classified according to their form, size,soundness, and the firmness with which they are held in place. This firmness is affectedby, among other factors, the length of time for which the branch was dead while theattaching stem continued to grow.Knots materially affect cracking (known in the industry as checking) and warping, ease inworking, and cleavability of timber. They are defects which weaken timber and lower itsvalue for structural purposes where strength is an important consideration. Theweakening effect is much more serious when timber is subjected to forces perpendicularto the grain and/or tension than where under load along the grain and/or compression.The extent to which knots affect the strength of a beam depends upon their position, size,number, direction of fiber, and condition. A knot on the upper side is compressed, whileone on the lower side is subjected to tension. If there is a season check in the knot, as isoften the case, it will offer little resistance to this tensile stress. Small knots, however,may be located along the neutral plane of a beam and increase the strength by preventinglongitudinal shearing. Knots in a board or plank are least injurious when they extendthrough it at right angles to its broadest surface. Knots which occur near the ends of abeam do not weaken it. Sound knots which occur in the central portion one-fourth theheight of the beam from either edge are not serious defects.Knots do not necessarily influence the stiffness of structural timber. Only defects of themost serious character affect the elastic limit of beams. Stiffness and elastic strength aremore dependent upon the quality of the wood fiber than upon defects in the beam. Theeffect of knots is to reduce the difference between the fiber stress at elastic limit and themodulus of rupture of beams. The breaking strength is very susceptible to defects. Soundknots do not weaken wood when subject to compression parallel to the grain.For purposes for which appearance is more important than strength, such as wallpanelling, knots are considered a benefit, as they add visual texture to the wood, giving ita more interesting appearance.The traditional style of playing the Basque xylophon txalaparta involves hitting the rightknots to obtain different tones.Plant anatomy, From Wikipedia, the free encyclopedia 190
  • 191. Heartwood and sapwoodA section of a Yew branch showing 27 annual growth rings, pale sapwood and darkheartwood, and pith (centre dark spot). The dark radial lines are small knots.Heartwood is wood that has died and become resistant to decay as a result of geneticallyprogrammed processes. It appears in a cross-section as a discolored circle, followingannual rings in shape. Heartwood is usually much darker than living wood, and formswith age. Many woody plants do not form heartwood, but other processes, such as decay,can discolor wood in similar ways, leading to confusion. Some uncertainty still exists asto whether heartwood is truly dead, as it can still chemically react to decay organisms,but only once (Shigo 1986, 54).Sapwood is living wood in the growing tree. All wood in a tree is first formed assapwood. Its principal functions are to conduct water from the roots to the leaves and tostore up and give back according to the season the food prepared in the leaves. The moreleaves a tree bears and the more vigorous its growth, the larger the volume of sapwoodrequired. Hence trees making rapid growth in the open have thicker sapwood for theirsize than trees of the same species growing in dense forests. Sometimes trees grown inthe open may become of considerable size, 30 cm or more in diameter, before anyheartwood begins to form, for example, in second-growth hickory, or open-grown pines.The term heartwood derives solely from its position and not from any vital importance tothe tree. This is evidenced by the fact that a tree can thrive with its heart completelydecayed. Some species begin to form heartwood very early in life, so having only a thinlayer of live sapwood, while in others the change comes slowly. Thin sapwood ischaracteristic of such trees as chestnut, black locust, mulberry, osage-orange, andsassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is therule.There is no definite relation between the annual rings of growth and the amount ofsapwood. Within the same species the cross-sectional area of the sapwood is very roughlyproportional to the size of the crown of the tree. If the rings are narrow, more of them arerequired than where they are wide. As the tree gets larger, the sapwood must necessarilyPlant anatomy, From Wikipedia, the free encyclopedia 191
  • 192. become thinner or increase materially in volume. Sapwood is thicker in the upper portionof the trunk of a tree than near the base, because the age and the diameter of the uppersections are less.When a tree is very young it is covered with limbs almost, if not entirely, to the ground,but as it grows older some or all of them will eventually die and are either broken off orfall off. Subsequent growth of wood may completely conceal the stubs which willhowever remain as knots. No matter how smooth and clear a log is on the outside, it ismore or less knotty near the middle. Consequently the sapwood of an old tree, andparticularly of a forest-grown tree, will be freer from knots than the heartwood. Since inmost uses of wood, knots are defects that weaken the timber and interfere with its ease ofworking and other properties, it follows that sapwood, because of its position in the tree,may have certain advantages over heartwood.It is remarkable that the inner heartwood of old trees remains as sound as it usually does,since in many cases it is hundreds of years, and in a few instances thousands of years,old. Every broken limb or root, or deep wound from fire, insects, or falling timber, mayafford an entrance for decay, which, once started, may penetrate to all parts of the trunk.The larvae of many insects bore into the trees and their tunnels remain indefinitely assources of weakness. Whatever advantages, however, that sapwood may have in thisconnection are due solely to its relative age and position.If a tree grows all its life in the open and the conditions of soil and site remainunchanged, it will make its most rapid growth in youth, and gradually decline. Theannual rings of growth are for many years quite wide, but later they become narrower andnarrower. Since each succeeding ring is laid down on the outside of the wood previouslyformed, it follows that unless a tree materially increases its production of wood from yearto year, the rings must necessarily become thinner as the trunk gets wider. As a treereaches maturity its crown becomes more open and the annual wood production islessened, thereby reducing still more the width of the growth rings. In the case of forest-grown trees so much depends upon the competition of the trees in their struggle for lightand nourishment that periods of rapid and slow growth may alternate. Some trees, such assouthern oaks, maintain the same width of ring for hundreds of years. Upon the whole,however, as a tree gets larger in diameter the width of the growth rings decreases.There may be decided differences in the grain of heartwood and sapwood cut from alarge tree, particularly one that is mature. In some trees, the wood laid on late in the lifeof a tree is softer, lighter, weaker, and more even-textured than that produced earlier, butin other species, the reverse applies. In a large log the sapwood, because of the time in thelife of the tree when it was grown, may be inferior in hardness, strength, and toughness toequally sound heartwood from the same log.Different woodsThere is a strong relationship between the properties of wood and the properties of theparticular tree that yielded it. For every tree species there is a range of density for thewood it yields. There is a rough correlation between density of a wood and its strength(mechanical properties). For example, while mahogany is a medium-dense hardwoodwhich is excellent for fine furniture crafting, balsa is light, making it useful for modelbuilding. The densest wood may be black ironwood.Wood is commonly classified as either softwood or hardwood. The wood from conifers(e.g. pine) is called softwood, and the wood from broad-leaved trees (e.g. oak) is calledPlant anatomy, From Wikipedia, the free encyclopedia 192
  • 193. hardwood. These names are a bit misleading, as hardwoods are not necessarily hard, andsoftwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softerthan any commercial softwood. Conversely, some softwoods (e.g. yew) are harder thanmost hardwoods.Wood products such as plywood are typically classified as engineered wood and notconsidered raw wood.ColourIn species which show a distinct difference between heartwood and sapwood the naturalcolour of heartwood is usually darker than that of the sapwood, and very frequently thecontrast is conspicuous. This is produced by deposits in the heartwood of variousmaterials resulting from the process of growth, increased possibly by oxidation and otherchemical changes, which usually have little or no appreciable effect on the mechanicalproperties of the wood. Some experiments on very resinous Longleaf Pine specimens,however, indicate an increase in strength. This is due to the resin which increases thestrength when dry. Such resin-saturated heartwood is called "fat lighter". Structures builtof fat lighter are almost impervious to rot and termites; however they are very flammable.Stumps of old longleaf pines are often dug, split into small pieces and sold as kindling forfires. Stumps thus dug may actually remain a century or more since being cut. Spruceimpregnated with crude resin and dried is also greatly increased in strength thereby.The wood of Coast Redwood is distinctively red in colourSince the late wood of a growth ring is usually darker in colour than the early wood, thisfact may be used in judging the density, and therefore the hardness and strength of thematerial. This is particularly the case with coniferous woods. In ring-porous woods thevessels of the early wood not infrequently appear on a finished surface as darker than thedenser late wood, though on cross sections of heartwood the reverse is commonly true.Except in the manner just stated the colour of wood is no indication of strength.Abnormal discolouration of wood often denotes a diseased condition, indicatingunsoundness. The black check in western hemlock is the result of insect attacks. Thereddish-brown streaks so common in hickory and certain other woods are mostly theresult of injury by birds. The discolouration is merely an indication of an injury, and in allprobability does not of itself affect the properties of the wood. Certain rot-producingfungi impart to wood characteristic colours which thus become symptomatic ofweakness; however an attractive effect known as spalting produced by this process isoften considered a desirable characteristic. Ordinary sap-staining is due to fungousgrowth, but does not necessarily produce a weakening effect.StructureWood is a heterogeneous, hygroscopic, cellular and anisotropic material. It is composedof fibers of cellulose (40% – 50%) and hemicellulose (15% – 25%) impregnated withlignin (15% – 30%).[2]Plant anatomy, From Wikipedia, the free encyclopedia 193
  • 194. Sections of tree trunkA tree trunk as found at the Veluwe, The NetherlandsIn coniferous or softwood species the wood cells are mostly of one kind, tracheids, and asa result the material is much more uniform in structure than that of most hardwoods.There are no vessels ("pores") in coniferous wood such as one sees so prominently in oakand ash, for example.Magnified cross-section of a diffuse-porous hardwood wood (Black Walnut), showingthe vessels, rays (white lines) and annual ringsThe structure of the hardwoods is more complex.[3] They are more or less filled withvessels: in some cases (oak, chestnut, ash) quite large and distinct, in others (buckeye,poplar, willow) too small to be seen plainly without a small hand lens. In discussing suchwoods it is customary to divide them into two large classes, ring-porous and diffuse-Plant anatomy, From Wikipedia, the free encyclopedia 194
  • 195. porous. In ring-porous species, such as ash, black locust, catalpa, chestnut, elm, hickory,mulberry, and oak, the larger vessels or pores (as cross sections of vessels are called) arelocalized in the part of the growth ring formed in spring, thus forming a region of more orless open and porous tissue. The rest of the ring, produced in summer, is made up ofsmaller vessels and a much greater proportion of wood fibres. These fibres are theelements which give strength and toughness to wood, while the vessels are a source ofweakness.In diffuse-porous woods the pores are scattered throughout the growth ring instead ofbeing collected in a band or row. Examples of this kind of wood are basswood, birch,buckeye, maple, poplar, and willow. Some species, such as walnut and cherry, are on theborder between the two classes, forming an intermediate group.Black locust end grain, showing the ring-porous structure.If a heavy piece of pine is compared with a light specimen it will be seen at once that theheavier one contains a larger proportion of late wood than the other, and is thereforeconsiderably darker. The late wood of all species is denser than that formed early in theseason, hence the greater the proportion of late wood the greater the density and strength.When examined under a microscope the cells of the late wood are seen to be very thick-walled and with very small cavities, while those formed first in the season have thin wallsand large cavities. The strength is in the walls, not the cavities. In choosing a piece ofpine where strength or stiffness is the important consideration, the principal thing toobserve is the comparative amounts of early and late wood. The width of ring is notnearly so important as the proportion of the late wood in the ring.It is not only the proportion of late wood, but also its quality, that counts. In specimensthat show a very large proportion of late wood it may be noticeably more porous andweigh considerably less than the late wood in pieces that contain but little. One can judgecomparative density, and therefore to some extent weight and strength, by visualinspection.Plant anatomy, From Wikipedia, the free encyclopedia 195
  • 196. The twisty branch of a Lilac treeNo satisfactory explanation can as yet be given for the real causes underlying theformation of early and late wood. Several factors may be involved. In conifers, at least,rate of growth alone does not determine the proportion of the two portions of the ring, forin some cases the wood of slow growth is very hard and heavy, while in others theopposite is true. The quality of the site where the tree grows undoubtedly affects thecharacter of the wood formed, though it is not possible to formulate a rule governing it. Ingeneral, however, it may be said that where strength or ease of working is essential,woods of moderate to slow growth should be chosen. But in choosing a particularspecimen it is not the width of ring, but the proportion and character of the late woodwhich should govern.In the case of the ring-porous hardwoods there seems to exist a pretty definite relationbetween the rate of growth of timber and its properties. This may be briefly summed upin the general statement that the more rapid the growth or the wider the rings of growth,the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, appliesonly to ring-porous woods such as oak, ash, hickory, and others of the same group, andis, of course, subject to some exceptions and limitations.In ring-porous woods of good growth it is usually the middle portion of the ring in whichthe thick-walled, strength-giving fibers are most abundant. As the breadth of ringdiminishes, this middle portion is reduced so that very slow growth producescomparatively light, porous wood composed of thin-walled vessels and woodparenchyma. In good oak these large vessels of the early wood occupy from 6 to 10 percent of the volume of the log, while in inferior material they may make up 25 per cent ormore. The late wood of good oak, except for radial grayish patches of small pores, is darkcolored and firm, and consists of thick-walled fibers which form one-half or more of thewood. In inferior oak, such fiber areas are much reduced both in quantity and quality.Such variation is very largely the result of rate of growth.Wide-ringed wood is often called "second-growth", because the growth of the youngtimber in open stands after the old trees have been removed is more rapid than in trees inthe forest, and in the manufacture of articles where strength is an important considerationsuch "second-growth" hardwood material is preferred. This is particularly the case in thechoice of hickory for handles and spokes. Here not only strength, but toughness andresilience are important. The results of a series of tests on hickory by the U.S. ForestService show that: "The work or shock-resisting ability is greatest in wide-ringed wood that has from 5 to 14 rings per inch (rings 1.8-5 mm thick), is fairly constant from 14 to 38 rings per inch (rings 0.7-1.8 mm thick), and decreases rapidly from 38 to 47 rings per inch (rings 0.5-0.7 mm thick). The strength at maximum load is not so great with the most rapid-growing wood; it is maximum with from 14 to 20 rings per inch (rings 1.3-1.8 mm thick), and again becomes less as the wood becomes more closely ringed. The natural deduction is that wood of first-class mechanical value shows from 5 to 20 rings per inch (rings 1.3-5 mm thick) and that slower growth yields poorer stock. Thus the inspector or buyer of hickory should discriminate against timber that has more than 20 rings per inch (rings less than 1.3 mm thick).Plant anatomy, From Wikipedia, the free encyclopedia 196
  • 197. Exceptions exist, however, in the case of normal growth upon dry situations, in which the slow-growing material may be strong and tough."[4]The effect of rate of growth on the qualities of chestnut wood is summarized by the sameauthority as follows: "When the rings are wide, the transition from spring wood to summer wood is gradual, while in the narrow rings the spring wood passes into summer wood abruptly. The width of the spring wood changes but little with the width of the annual ring, so that the narrowing or broadening of the annual ring is always at the expense of the summer wood. The narrow vessels of the summer wood make it richer in wood substance than the spring wood composed of wide vessels. Therefore, rapid-growing specimens with wide rings have more wood substance than slow-growing trees with narrow rings. Since the more the wood substance the greater the weight, and the greater the weight the stronger the wood, chestnuts with wide rings must have stronger wood than chestnuts with narrow rings. This agrees with the accepted view that sprouts (which always have wide rings) yield better and stronger wood than seedling chestnuts, which grow more slowly in diameter."[4]In diffuse-porous woods, as has been stated, the vessels or pores are scattered throughoutthe ring instead of collected in the early wood. The effect of rate of growth is, therefore,not the same as in the ring-porous woods, approaching more nearly the conditions in theconifers. In general it may be stated that such woods of medium growth afford strongermaterial than when very rapidly or very slowly grown. In many uses of wood, strength isnot the main consideration. If ease of working is prized, wood should be chosen withregard to its uniformity of texture and straightness of grain, which will in most casesoccur when there is little contrast between the late wood of one seasons growth and theearly wood of the next.Monocot woodStructural tissue resembling ordinary dicot wood is produced by a number of monocotplants, and these are also usually called wood. Of these, the wood of the grass bamboohas considerable economic importance, larger culms being used in the manufacture ofengineered flooring, panels and veneer. Other plant groups that produce woody tissue arepalms, and members of the Liliales, such as Dracaena and Cordyline. With all thesewoods, the structure and composition of the structural tissue is quite different fromordinary wood.Water contentPlant anatomy, From Wikipedia, the free encyclopedia 197
  • 198. The churches of Kizhi, Russia are among a handful of World Heritage Sites built entirelyof wood, without metal joints.Water occurs in living wood in three conditions, namely: (1) in the cell walls, (2) in theprotoplasmic contents of the cells, and (3) as free water in the cell cavities and spaces. Inheartwood it occurs only in the first and last forms. Wood that is thoroughly air-driedretains from 8-16% of water in the cell walls, and none, or practically none, in the otherforms. Even oven-dried wood retains a small percentage of moisture, but for all exceptchemical purposes, may be considered absolutely dry.The general effect of the water content upon the wood substance is to render it softer andmore pliable. A similar effect of common observation is in the softening action of wateron paper or cloth. Within certain limits, the greater the water content, the greater itssoftening effect.Drying produces a decided increase in the strength of wood, particularly in smallspecimens. An extreme example is the case of a completely dry spruce block 5 cm insection, which will sustain a permanent load four times as great as that which a greenblock of the same size will support.The greatest increase due to drying is in the ultimate crushing strength, and strength atelastic limit in endwise compression; these are followed by the modulus of rupture, andstress at elastic limit in cross-bending, while the modulus of elasticity is least affected.UsesFuel Main article: Wood fuelWood is burned as a fuel mostly in rural areas of the world. Hard wood is preferred oversoftwood because it creates less smoke and burns longer. Adding a woodstove orfireplace to a home adds ambiance and warmth.[5]ConstructionWood can be cut into straight planks and made into a hardwood floor (parquetry).Plant anatomy, From Wikipedia, the free encyclopedia 198
  • 199. The Saitta House, Dyker Heights, Brooklyn, New York built in 1899 is made of anddecorated in wood.Wood has been an important construction material since humans began building shelters,houses and boats. Nearly all boats were made out of wood till the late 19th century, andwood remains in common use today in boat construction. New domestic housing in manyparts of the world today is commonly made from timber-framed construction. Inbuildings made of other materials, wood will still be found as a supporting material,especially in roof construction, in interior doors and their frames, and as exteriorcladding. Wood to be used for construction work is commonly known as lumber in NorthAmerica. Elsewhere, lumber usually refers to felled trees, and the word for sawn planksready for use is timber.Wood unsuitable for construction in its native form may be broken down mechanically(into fibres or chips) or chemically (into cellulose) and used as a raw material for otherbuilding materials such as chipboard, engineered wood, hardboard, medium-densityfiberboard (MDF), oriented strand board (OSB). Such wood derivatives are widely used:wood fibers are an important component of most paper, and cellulose is used as acomponent of some synthetic materials. Wood derivatives can also be used for kinds offlooring, for example laminate flooring.Wood is also used for cutlery, such as chopsticks, toothpicks, and other utensils, like thewooden spoon.See also • List of woods • Lumber • XylophagyNotes 1. ^ Wood growth and structure www.farmforestline.com.au 2. ^ Lesson 1: Tree Growth and Wood Material at University of Minnesota Extension 3. ^ Hardwood Structure www.uwsp.edu 4. ^ a b U.S. Department of Agriculture, Forest Products Laboratory. The Wood Handbook: Wood as an engineering material. General Technical Report 113. Madison, WI. 5. ^ Clean Burning Wood Stoves and FireplacesPlant anatomy, From Wikipedia, the free encyclopedia 199
  • 200. References Wikimedia Commons has media related to: WoodLook up Wood inWiktionary, the free dictionary. • Hoadley, R. Bruce (2000). Understanding Wood: A Craftsman’s Guide to Wood Technology. Taunton Press. ISBN 1-56158-358-8. • Shigo, Alex. (1986) A New Tree Biology Dictionary. Shigo and Trees, Associates. ISBN 0-943563-12-7 • The Wood in Culture AssociationList of woodsThis is a list of woods, in particular those commonly used in the timber and lumber trade.See also: woods (golf clubs), forest, and the list of forests.Contents • 1 Softwoods (conifers) • 2 Hardwoods (angiosperms) • 3 Hardwoods (monocotyledons) • 4 See also • 5 External linksSoftwoods (conifers) • Araucaria o Hoop Pine (Aus.) Araucaria cunninghamii o Parana Pine (Brazil) Araucaria angustifolia o Pehuén or Chile Pine Araucaria araucana • Cedar (Cedrus); also applied to a number of woods from trees in the Cypress family mainly in North America, see Redcedar, Whitecedar and Yellow-Cedar in Softwoods, and to woods from some relatives of the mahogany, see Spanish-cedar and Redcedar in Hardwoods • Cypress (Chamaecyparis, Cupressus, Taxodium) o Arizona Cypress (Cupressus arizonica) o Bald Cypress or Southern cypress (Taxodium distichum) o Hinoki Cypress (Chamaecyparis obtusa) o Lawsons Cypress (Chamaecyparis lawsoniana) o Mediterranean Cypress (Cupressus sempervirens) • Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) • European Yew (Taxus baccata) • Fir (Abies) o Balsam Fir (Abies balsamea) o Silver Fir (Abies alba) o Noble Fir (Abies procera) o Pacific Silver Fir (Abies amabilis)Plant anatomy, From Wikipedia, the free encyclopedia 200
  • 201. • Hemlock (Tsuga) o Eastern Hemlock (Tsuga canadensis) o Mountain Hemlock (Tsuga mertensiana) o Western Hemlock (Tsuga heterophylla) • Kauri (New Zealand) (Agathis australis) • Kaya (Torreya nucifera) • Larch (Larix) o European Larch (Larix decidua) o Japanese Larch (Larix kaempferi) o Tamarack Larch or Tamarack (Larix laricina) o Western Larch (Larix occidentalis) • Pine (Pinus; Many woods are incorrectly called "Pine". See Araucaria and Douglas-fir above) o Corsican pine (Pinus nigra) o Jack Pine (Pinus banksiana) o Lodgepole Pine (Pinus contorta subsp latifolia) o Monterey Pine (Pinus radiata) o Ponderosa Pine (Pinus ponderosa) o Red Pine (N.Am.) (Pinus resinosa) o Scots Pine, Red pine (UK), Red deal (UK), Redwood (UK, obsolete) (Pinus sylvestris) o White Pine in (N.Am.), Yellow or Weymouth pine (UK, obsolete) Eastern White Pine (Pinus strobus) Western White Pine (Pinus monticola) Sugar Pine (Pinus lambertiana) o Southern Yellow pine (US) Loblolly Pine (Pinus taeda) Longleaf Pine (Pinus palustris) Pitch Pine (Pinus rigida) Shortleaf Pine (Pinus echinata) • "Redcedar" o Eastern Redcedar, (Juniperus virginiana) o Western redcedar (Thuja plicata) • Redwood (Sequoia sempervirens) • Rimu (New Zealand) (Dacrydium cupressinum) • Spruce (Picea) o Norway Spruce (Picea abies) o Black Spruce (Picea mariana) o Red Spruce (Picea rubens) o Sitka Spruce (Picea sitchensis) o White Spruce (Picea glauca) • Sugi (Cryptomeria japonica) • "Whitecedar" o Northern Whitecedar (Thuja occidentalis) o Southern Whitecedar (Chamaecyparis thyoides)Plant anatomy, From Wikipedia, the free encyclopedia 201
  • 202. • "Yellow-cedar" (Nootka Cypress Callitropsis nootkatensis, formerly Chamaecyparis nootkatensis)Hardwoods (angiosperms) • Afzelia (Afzelia) • Agba yun (Synsepalum duloificum) • Albizia (Albizia) • Alder (Alnus) o Black alder (Alnus glutinosa) o Red alder (Alnus rubra) • Applewood or wild apple (Malus) • Ash (Fraxinus) o Black ash (Fraxinus nigra) o Blue ash (Fraxinus quadrangulata) o Common ash (Fraxinus excelsior) o Green ash (Fraxinus pennsylvanica lanceolata) o White ash (Fraxinus americana) • Aspen (Populus) o American aspen (Populus tremuloides) o Bigtooth aspen (Populus grandidentata) o European aspen (Populus tremula) • Ayan (Distemonanthus benthamianus) • Balsa (Ochroma pyramidale) • Basswood (Tilia americana) • Beech (Fagus) o European Beech (Fagus sylvatica) o American Beech (Fagus grandifolia) • Birch (Betula) o American birches Gray birch (Betula populifolia) Paper birch (Betula papyrifera) Sweet birch (Betula lenta) Yellow birch (B. alleghaniensis syn Betula lutea) - most common birch wood sold in N.Am. o European birches, also Baltic birch (N.Am.) Silver birch (Betula pendula) White Birch (Betula pubescens) • Blackbean (Castanospermum australe) • Blackwood o Australian Blackwood also Tasmanian Blackwood (Acacia melanoxylon) o African Blackwood or Mpingo (Dalbergia melanoxylon) • Bocote (Cordia alliodora) • Boxwood or Box (Buxus sempervirens) • Brazilwood (Caesalpinia echinata) • Bubinga (Guibourtia) • Buckeye (Aesculus) o Common Horse-chestnut (Aesculus hippocastanum)Plant anatomy, From Wikipedia, the free encyclopedia 202
  • 203. o Yellow Buckeye (Aesculus flava) • Butternut (Juglans cinerea) • Carapa (or Andiroba, Carap, Crappo, Crabwood and Santa Maria) (Carapa guianensis) . • Catalpa (Catalpa) • Cherry (Prunus) o Black cherry (Prunus serotina) o Red cherry (Prunus pennsylvanica) o Wild cherry (Prunus avium) o "Brazilian Cherry" Not a Cherry See Jatoba below • Chestnut (Castanea dentata) o Cape Chestnut (Calodendrum capense) • Coachwood (Ceratopetalum apetalum) • Cocobolo (Dalbergia retusa) • Corkwood (Leitneria floridana) • Cottonwood, eastern (Populus deltoides) • Dogwood (Cornus spp.) • Ebony (Diospyros) o Andaman marble-wood (India) (Diospyros kurzii) o Ebène marbre (Mauritius, E. Africa) (Diospyros melanida) o Gabon ebony, Black ebony, African ebony (Diospyros crassiflora) • Elm o American elm (Ulmus americana) o English elm (Ulmus procera) o Rock elm (Ulmus thomasii) o Slippery elm (Ulmus rubra) o Wych elm (Ulmus glabra) • Eucalyptus (Eucalyptus) o Lyptus o Karri (W. Australia) (Eucalyptus diversicolor) o Mahogany eucalyptus, (New South Wales) (Eucalyptus) o Ironbark Eucalyptus sideroxylon o Jarrah or West Australian eucalyptus (Eucalyptus marginata) o Tasmanian oak or Mountain ash, (Eucalyptus regnans Eucalyptus obliqua Eucalyptus delegatensis) o River Red Gum o Blue Gum Eucalyptus saligna • Greenheart (Guyana) (Chlorocardium rodiei) • Grenadilla (Mpingo) (Dalbergia melanoxylon) • Gum o Blackgum (Nyssa sylvatica) o Blue gum (Eucalyptus globulus) o Redgum or Sweetgum (Liquidambar styraciflua) o Tupelo gum (Nyssa aquatica) • Hickory (Carya) o Mockernut hickory (Carya alba)Plant anatomy, From Wikipedia, the free encyclopedia 203
  • 204. o Pignut hickory (Carya glabra) o Shagbark hickory (Carya ovata) o Shellbark hickory (Carya laciniosa) • Hornbeam (Carpinus species) • Hophornbeam, Eastern (Ostrya virginiana) • Ipê or Poui (Tabebuia) • Iroko (Milicia excelsa syn Chlorophora excelsa) • Ironwood refers to the wood of many tree species noted for the hardness of their wood. Trees commonly known as ironwoods include: o Carpinus caroliniana — also known as American hornbeam o Casuarina equisetifolia — Common Ironwood from Australia o Choricbangarpia subargentea o Copaifera spp. o Eusideroxylon zwageri o Guajacum officinale and Guajacum sanctum — Lignum vitae o Hopea odorata o "Ipe High in silica this wood makes a great decking material. Other common name " Brazilian Walnut" o Krugiodendron ferreum — Black Ironwood o Lyonothamnus lyonii (L. floribundus) — Catalina Ironwood o Mesua ferrea — also known as Rose Chestnut or Ceylon Ironwood, from Thailand, Laos, Vietnam, Cambodia o Olea spp. — various olive trees o Olneya tesota — Desert Ironwood o Ostrya virginiana — Hop hornbeam o Parrotia persica — Persian Ironwood o Tabebuia serratifolia — Yellow Lapacho • Jacarandá, Brazilian rosewood (Dalbergia nigra) • Jatobá (Hymenaea courbaril) • Lacewood from the Sycamore(N.Am.) or Plane(UK) trees (Platanus species) • Laurel, California (Umbellularia californica) • Limba (Terminalia superba) • Lignum vitae (Guaiacum officinale and Guaiacum sanctum) • Locust o Black locust or Yellow locust (Robinia pseudacacia) o Honey locust (Gleditsia triacanthos) • Mahogany • Maple (Acer) o Hard Maple (N.Am.) Sugar maple (Acer saccharum) Black maple (Acer nigrum) o Soft Maple (N.Am.) Manitoba maple (Acer negundo) Red maple (Acer rubrum) Silver maple (Acer saccharinum) o European MaplesPlant anatomy, From Wikipedia, the free encyclopedia 204
  • 205. Sycamore maple (Acer pseudoplatanus) • Meranti (Shorea spp.) • Mpingo (Grenadilla) (Dalbergia melanoxylon) • Oak (Quercus) o American White Oak includes wood from any of the following species of trees: Bur oak (Quercus macrocarpa) White oak (Quercus alba) Post oak (Quercus stellata) Swamp white oak (Quercus bicolor) Southern live oak (Quercus virginiana) Swamp chestnut oak (Quercus michauxii) Chestnut oak (Quercus prinus or Q. Montana) Chinkapin oak (Quercus muhlenbergii) Canyon live oak (Quercus chrysolepis) Overcup oak (Quercus lyrata) o English oak, also French and Slovenian oak barrels (Quercus robur and sometimes Quercus petraea) o Red oak includes wood from any of the following species of trees: Red oak (Quercus rubra) Black oak (Quercus velutina) Laurel oak (Quercus laurifolia)) Southern red oak (Quercus falcata) Water oak (Quercus nigra) Willow oak {Quercus phellos) Nuttalls oak (Quercus texana or Q. nuttallii) Willow oak (Quercus phellos) o "Tasmanian oak"; Not an oak see Eucalyptus above o Australian "Silky oak"; Not an oak see Silky Oak below • Obeche or Samba, Ayous, Arere, Wana, Abache (West Africa) (Triplochiton scleroxylon) • Okoumé or "Gaboon" (Aucoumea klaineana) • Oregon Myrtle or California Bay Laurel (Umbellularia californica) • Pear (Pyrus communis) • Pernambuco is another name for Brazilwood (Caesalpinia echinata) • Poplar (Populus; in N.Am., wood sold as poplar is usually Yellow-poplar — see below) o Balsam poplar (Populus balsamifera) o Black poplar (Populus nigra) o Hybrid poplar (Populus × canadensis) • Ramin • Redcedar (Toona ciliata) • Rosewood (Dalbergia spp.) • Sal (Shorea robusta) • Sandalwood (Santalum) • Sassafras (Sassafras albidum)Plant anatomy, From Wikipedia, the free encyclopedia 205
  • 206. • Sassafras (Australia) (Atherosperma moschatum) • Satinwood (Ceylon) (Chloroxylon swietenia) • Silky Oak (Grevillea robusta) - Sold as Lacewood in North America • Silver Wattle Acacia dealbata • Snakewood • Sourwood (Oxydendrum arboreum) • Spanish-cedar (Cedrela odorata) • American sycamore (Platanus occidentalis) • Teak (Tectona grandis) • Walnut (Juglans) o Black Walnut (Juglans nigra) o Persian Walnut (Juglans regia) o Brazilian walnut; Not a walnut see Ipe above. • Willow (Salix) o Black willow (Salix nigra) o Cricket-bat willow (Salix alba Coerulea) o White willow (Salix alba) • Yellow-poplar (Liriodendron tulipifera)Hardwoods (monocotyledons) • Bamboo (a number of species in Tribe: Bambuseae) • Palmwood (Cocos nucifera) is new wood source that is increasingly being used as an ecologically-sound alternative to endangered hardwoods.See also • List of Indian timber trees • WoodExternal links • Wood Identification Website • Database of Wood Species • Australian timbers • Reproduction of The American Woods: exhibited by actual specimens and with copious explanatory text by Romeyn B. Hough • US Forest Products Laboratory, "Characteristics and Availability of Commercially Important Wood" from the Wood Handbook PDF 916K • International Wood Collectors Society • Xiloteca Manuel Soler (One of the largest private collection of wood samples)Plant anatomy, From Wikipedia, the free encyclopedia 206
  • 207. Lumber The examples and perspective in this article or section may not represent a worldwide view of the subject. Please improve this article or discuss the issue on the talk page."Timber" redirects here. For other uses, see Timber (disambiguation). Timber in storage for later processing at a sawmill Lumber or timber is wood in any of its stages from felling through readiness for use as structural material for construction, or wood pulp for paper production. Timber often refers to the wood contents of standing, live trees that can be used for lumber or fiber production, although it can also be used to describe sawn lumber whose smallest dimension is not lessthan 5 inches (127 mm).[1] Wood cut from Victorian Mountain Ash Lumber is supplied either rough or finished. Besides pulpwood, rough lumber is the raw material for furniture-making and other items requiring additional cutting and shaping. It is available in many species, usually hardwoods. Finished lumber is supplied in standard sizes, mostly for the construction industry, primarily softwood from coniferous species includingpine, cedar, hemlock, fir and spruce, but also some hardwood for high-grade flooring.Contents • 1 Dimensional lumber o 1.1 Non-North American sizes o 1.2 Hardwoods o 1.3 Engineered lumber • 2 Defects in lumber o 2.1 Defects due to conversion o 2.2 Defects due to fungi o 2.3 Defects due to insects o 2.4 Defects due to natural forces o 2.5 Defects due to seasoning • 3 Preservatives • 4 Timber framing • 5 Terminology • 6 See also • 7 References • 8 External linksDimensional lumberDimensional lumber is a term used for lumber that is finished/planed and cut tostandardized width and depth specified in inches. Examples of common sizes are 2×4Plant anatomy, From Wikipedia, the free encyclopedia 207
  • 208. (also two-by-four and other variants such as four-b-two in England, Australia, NewZealand), 2×6, and 4×4. The length of a board is usually specified separately from thewidth and depth. It is thus possible to find 2×4s that are four, eight, or twelve feet inlength. In the United States the standard lengths of lumber are 6, 8, 10, 12, 14, 16, 18, 20,22, and 24 feet.North American softwood dimensional lumber sizesNominal Actual Nominal Actual Nominal Actual 31×2 ⁄4 in × 11⁄2 in (19 2 × 2 11⁄2 in × 11⁄2 in 4×4 31⁄2 in × 31⁄2 in mm × 38 mm) (38 mm × 38 mm) (89 mm × 89 mm) 3 1 1 1 31⁄2 in × 51⁄2 in1×3 ⁄4 in × 2 ⁄2 in (19 2 × 3 1 ⁄2 in × 2 ⁄2 in 4×6 (89 mm × 140 mm × 64 mm) (38 mm × 64 mm) mm) 3 51⁄2 in × 51⁄2 in1×4 ⁄4 in × 31⁄2 in (19 2 × 4 11⁄2 in × 31⁄2 in 6×6 (140 mm × 140 mm × 89 mm) (38 mm × 89 mm) mm) 3 11⁄2 in × 51⁄2 in 71⁄4 in × 71⁄4 in1×6 ⁄4 in × 51⁄2 in (19 2 × 6 (38 mm × 140 8 × 8 (184 mm × 184 mm × 140 mm) mm) mm) 3 11⁄2 in × 71⁄4 in1×8 ⁄4 in × 71⁄4 in (19 2 × 8 (38 mm × 184 mm × 184 mm) mm) 3 11⁄2 in × 91⁄4 in1 × 10 ⁄4 in × 91⁄4 in (19 2 × 10 (38 mm × 235 mm × 235 mm) mm) 3 ⁄4 in × 111⁄4 in 11⁄2 in × 111⁄4 in1 × 12 (19 mm × 286 2 × 12 (38 mm × 286 mm) mm)Solid dimensional lumber typically is only available up to lengths of 24 ft, yet sincebuilders have a need for lengths beyond that for roof construction (rafters), builders use"finger-jointed" lumber that can be up to 36 ft long in 2×6 size (see Engineered Lumberbelow). Finger-jointed lumber is also widely used for smaller lengths like studs, thevertical members of a framed wall. Pre-cut studs save a framer a lot of time as they arepre-cut by the manufacturer to be used in 8 ft, 9 ft & 10 ft ceiling applications, whichmeans they have removed a few inches of the piece to allow for the sill plate and thedouble top plate with no additional sizing necessary by the framer.In the Americas, two-bys (2×4s, 2×6s, 2×8s, 2×10s, and 2×12s), along with the 4×4, arecommon lumber sizes used in modern construction. They are the basic building block forsuch common structures as balloon-frame or platform-frame housing. Dimensionallumber made from softwood is typically used for construction, while hardwood boardsare more commonly used for making cabinets or furniture.The nominal size of a board varies from the actual size of the board. This is due toplaning and shrinkage as the board is dried.[citation needed] This results in the final lumberPlant anatomy, From Wikipedia, the free encyclopedia 208
  • 209. being slightly smaller than the nominal size. Also, if the wood is surfaced when it isgreen, the initial dimensions are slightly larger (e.g. 1⁄16 in bigger for up to 4 in nominallumber, ⅛ in for 5 in and 6 in nominal lumber, ¼ in bigger for larger sizes). As the wooddries, it shrinks and reaches the specified actual dimensions.Non-North American sizesExamples of dimensional lumber sizes(softwood and hardwood)Inch name Sawed Swedish Australian2×4 50 mm × 100 mm 45 mm × 95 mm 45 mm × 90 mm1×3 25 mm × 75 mm 22 mm × 70 mm 19 mm × 70 mm3×3 75 mm × 75 mm 70 × 70 mm2×7 50 mm × 175 mm 45 mm × 170 mm Not used2×3 50 mm × 75 mm 45 mm × 70 mm 45 mm × 70 mm1×4 25 mm × 100 mm 22 mm × 95 mm 19 mm × 90 mm1×5 25 mm × 125 mm 22 mm × 120 mm 19 mm × 120 mm2×5 50 mm × 125 mm 45 mm × 120 mm 45 mm × 120 mmOutside North America sizes of timber can vary slightly. Sizes are, in some cases, basedon the imperial measurement and referred to as such; in other cases the sizes are too farremoved from the imperial size to be referred to by imperial measurement. Lengths aresold every 300 mm (a metric approximation of 1 ft). Common sizes are similar to theNorth American equivalent; 2.4, 2.7, 3.0, 3.6, 4.2, 4.8, 5.4, 6.0.HardwoodsHardwood dimensional lumber sizesNominal Surfaced 1 Side (S1S) Surfaced 2 sides (S2S)1 3 5 ⁄2 in ⁄8 in ⁄16 in5 1 7 ⁄8 in ⁄2 in ⁄16 in3 5 9 ⁄4 in ⁄8 in ⁄16 in 4 7 131 in or ⁄4 in ⁄8 in ⁄16 in11⁄4 in or 5⁄4 in 11⁄8 in 11⁄16 in11⁄2 in or 6⁄4 in 13⁄8 in 15⁄16 in2 in or 8⁄4 in 113⁄16 in 13⁄4 in3 in or 12⁄4 in 213⁄16 in 23⁄4 in4 in or 16⁄4 in 313⁄26 in 33⁄4 inIn North America sizes for dimensional lumber made from hardwoods varies from thesizes for softwoods. Boards are usually supplied in random widths and lengths of aPlant anatomy, From Wikipedia, the free encyclopedia 209
  • 210. specified thickness, and sold by the board-foot (144 cubic inches, 1⁄12th of a cubic foot).This does not apply in all countries, for example in Australia many boards are sold totimber yards in packs with a common profile (dimensions) but not necessarily ofconsisting of the same length boards. Hardwoods cut for furniture are cut in the fall andwinter, after the sap has stopped running in the trees. If hardwoods are cut in the spring orsummer the sap ruins the natural color of the timber and deteriorates the value of thetimber for furniture.Also in North America hardwood lumber is commonly sold in a “quarter” system whenreferring to thickness. 4/4 (four quarters) refers to a one-inch thick board, 8/4 (eightquarters) is a two-inch thick board, etc. This system is not usually used for softwoodlumber, although softwood decking is sometimes sold as 5/4 (actually one inch thick).Engineered lumberEngineered lumber is lumber created by a manufacturer and designed for a certainstructural purpose. The main categories of engineered lumber are:[2] 1. Laminated Veneer Lumber (LVL) – LVL comes in 13⁄4 inch thicknesses with depths such as 91⁄2, 117⁄8, 13, 16, 18, or 24 inches, and are typically doubled or tripled up. They function as beams to provide support over large spans, such as removed support walls and garage door openings, places where dimensional lumber isnt structurally sound to use, and also in areas where a heavy load is bearing from a floor, wall or roof above on a somewhat short span where dimensional lumber isnt practical. This type of lumber cannot be altered by holes or notches anywhere within the span or at the ends, as it compromises the integrity of the beam, but nails can be driven into it wherever necessary to anchor the beam or to add hangers for I-joists or dimensional lumber joists that terminate at an LVL beam. 2. Wood I-joists – Sometimes called "TJI®" or "Trus Joists®", both of which are brands of wood I-joists, they are used for floor joists on upper floors and also in first floor conventional foundation construction on piers as opposed to slab floor construction. They are engineered for long spans and are doubled up in places where a wall will be placed over them, and sometimes tripled where heavy roof- loaded support walls are placed above them. They consist of a top and bottom chord/flange made from LVL with a webbing in-between made from oriented strand board (OSB). The webbing can be removed up to certain sizes/shapes according to the manufacturers or engineers specifications, but for small holes, wood I-joists come with "knockouts", which are perforated, precut areas where holes can be made easily, typically without engineering approval. When large holes are needed, they can typically be made in the webbing only and only in the center third of the span; the top and bottom chords cannot be cut. Sizes and shapes of the hole, and typically the placing of a hole itself, must be approved by an engineer prior to the cutting of the hole and in many areas, a sheet showing the calculations made by the engineer must be provided to the building inspection authorities before the hole will be approved. Some I-joists are made with W-style webbing like a truss to eliminate cutting and allow ductwork to pass through.Plant anatomy, From Wikipedia, the free encyclopedia 210
  • 211. Freshly cut logs showing sap running from beneath bark 3. Finger-Jointed Lumber – Solid dimensional lumber lengths typically are limited to lengths of 22 to 24 feet, but can be made longer by the technique of "finger- jointing" lumber by using small solid pieces, usually 18 to 24 inches long, and joining them together using finger joints and glue to produce lengths that can be up to 36 feet long in 2×6 size. Finger-jointing also is predominant in precut wall studs. 4. Glu-lam Beams – Created from 2×4 or 2×6 stock by gluing the faces together to create beams such as 4×12 or 6×16. LVL beams have taken their place in most home construction. 5. Manufactured Trusses – Trusses are used in home construction as bracing to support the roof rafters in the attic space. It is seen as an easier installation and a better solution for supporting roofs as opposed to the use of dimensional lumbers struts and purlins as bracing. In the southern USA and other parts, stick-framing with dimensional lumber roof support is still predominant. The main drawback of trusses is that less attic space is usable. 6. Oriented Strand Board (OSB) – OSB is made by laminating large, thin wood chips with glue, such that the grain orientation of the chips is random, making the OSB panels equally stiff in all directions. OSB has replaced plywood for use as exterior wall sheathing and roof decking (7⁄16 inch minimum thickness) and in second-story flooring (3⁄4 inch thickness in a tongue-and-groove interlocking pattern), which is nailed and glued to the I-joists. OSB used in wall sheathing and roof decking will swell if exposed to the elements for even a brief time and must be replaced; therefore, it is covered by a weatherproof membrane such as felt or spun-bonded olefin (Tyvek®) to protect it, secured with plastic cap nails. House wrapping is used on areas which will be sheathed with vinyl siding. 3⁄4 inch tongue-and-groove OSB flooring is coated to protect it from the elements for a short time until the structure is roofed over. Moisture resistant OSB is often specified for use as a roof underlayment.Defects in lumberDefects occurring in Timber are grouped into the following five divisions:Defects due to conversionDuring the process of converting timber to commercial form, the following defects mayoccur: 1. Chip mark 2. Diagonal grainPlant anatomy, From Wikipedia, the free encyclopedia 211
  • 212. 3. Torn grain 4. WaneDefects due to fungiFungi attack timber only when the following two conditions are satisfied simultaneously: 1. The moisture content of the timber is above 20% 2. There is presence of air and warmth for the growth of fungi.If any of the above condition is absent, decay of wood due to fungi would not occur.Hence, dry wood due having moisture content less than 20 per cent will remain sound forcenturies. Similarly, wood submerged in water will not be attacked by fungi because ofabsence of air. Following defects are caused in timber by fungi: 1. Blue stain 2. Brown rot 3. Dry rot 4. Heart rot 5. Sap stain 6. Wet rot 7. White rotDefects due to insectsFollowing are the insects which are usually responsible for the decay of timber: 1. Beetles 2. Marine Borers 3. Termites 4. Mountain Pine BeetleDefects due to natural forcesThe main natural forces responsible for causing defects in timber are two, namely,abnormal growth and rupture of tissues.Defects due to seasoningDefects due to seasoning are the number one cause for splinters and slivers.Preservatives Main article: timber treatment Fasteners used with treated lumber require special consideration because of the corrosive chemicals used in the treatment process. Timber or lumber may be treated with a preservative that protects it from being destroyed by insects, fungus or exposure to moisture. Generally this is applied through combined vacuum and pressure treatment. The preservatives used to pressure-treat lumber are classified as pesticides; due to potential hazards to humans and the environment, some are being phased out. Treating lumber provides long-term resistance to organisms that cause deterioration. If it is applied correctly, it extends the productive life of lumber by five to ten times. If leftPlant anatomy, From Wikipedia, the free encyclopedia 212
  • 213. untreated, wood that is exposed to moisture or soil for sustained periods of time willbecome weakened by various types of fungi, bacteria or insects.Timber framing Main article: timber framingTimber framing is a style of construction which uses heavier framing elements thanmodern stick framing, which uses dimensional lumber. The timbers originally were treeboles squared with a broadaxe or adze and joined together with joinery without nails. Amodern imitation with sawn timbers is growing in popularity in the United States.One of the most conventional framing methods is the Neumann Notch, which involves athirty-two degree angling of adjoining lumber and then a right-angled wedge with aneighteen degree cusp fitted between the lumber before being bolted. This convention waspioneered by Daniel R. Neumann, a carpenter from Germany, that was responsible for thestructural development of the Massachusetts Bay Colony in 1630. This framingconvention spread to construction sites in other colonies, most famously Plymouth andConcord. Neumanns notched framing then was adopted by carpenters and constructioncompanies and this framing convention is still used today in traditional frame sets.[citationsneeded]Another somewhat less conventional method for framing is known as the "New-style"binding. The basic setup of the New-style binding was developed by Austin D. New, aMormon settler in Salt Lake City, Utah during the 1800s. The basic structure of the New-style binding involves a set-up of two similar sized logs set against each otherperpendicularly and lashed together with hemp rope. This technique was used toconstruct many of the early houses of the Mormon settlers due to its ease of use anddurability. Eventually the New-style binding became obsolete as the settlers beganconstructing homes out of the more traditional brick and mortar.TerminologyIn the United Kingdom and Australia, "timber" is a term also used for sawn woodproducts (that is, boards), whereas generally in the United States and Canada, the productof timber cut into boards is referred to as lumber. In the United States and Canada sawnwood products of five inches (127 mm) (nominal size) diameter or greater are sometimescalled "timbers".See also • British timber trade • Deck (building) • Forestry • Hardwood timber production • Hartwick Pines State Park • Illegal logging • Interlochen State Park • List of Indian timber trees • List of woods • Log scaler • Logging • Lumber baron • Lumber room • Lumbermans MonumentPlant anatomy, From Wikipedia, the free encyclopedia 213
  • 214. • Michigan logging wheels • Non-timber forest products • Plank • Recycling timber • Sawmill • Saw pit • Sodium silicates use as a timber treatment • Timber treatment • United States-Canada softwood lumber dispute • Wood • Woody plant • WoodworkingReferences 1. ^ "Conceptual Reference Database for Building Envelope Research". Retrieved on 2008- 03-28. 2. ^ "Austin Energy page describing engineered structural lumber". Retrieved on 2006-09- 10. This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (September 2006)External linksLook up lumber, timber in Wiktionary, the free dictionary. • Hills Brothers Long Log Harvesting Archive Footage • Hills Brothers Short Log Harvesting Archive Footage • National Hardwood Lumber Association • Timber Development Association of NSW - Australia • CPSC Test coatings to reduce arsenic emissions from pressure treated wood • TRADA: Timber Research And Development Association • Wood themed links and activities • Lumber Directory • The Forest Products Laboratory. US main wood products research lab. Madison, WI (E) • International Wood Collectors Society • Xiloteca Manuel Soler (One of the largest private collection of wood samples) • Humanitarian Timber project (A project to produce and disseminate a field handbook that brings together best practice in the procurement and use of timber in humanitarian emergencies)Retrieved from "http://en.wikipedia.org/wiki/Lumber"Categories: Forestry | Timber industry | WoodHidden categories: Articles with limited geographic scope | All articles with unsourcedstatements | Articles with unsourced statements since June 2008 | Articles with unsourcedstatements since March 2008 | Articles needing additional references from September2006Plant anatomy, From Wikipedia, the free encyclopedia 214
  • 215. Xylophagy Not to be confused with XylophagiaWorker termiteXylophagy is a term used in ecology to describe the habits of an herbivorous animalwhose diet consists primarily (often solely) of wood. The word derives from Greekξυλοφάγος (xulophagos) "eating wood", from ξύλον (xulon) "wood" + φάγειν (phagein)"to eat" and it was an ancient Greek name for a kind of a worm[1].Xylophagous insectsMost such animals are arthropods, primarily insects of various kinds, in which thebehavior is quite common, and found in many different orders. It is not uncommon forinsects to specialize to various degrees; in some cases, they limit themselves to certainplant groups (a taxonomic specialization), and in others, it is the physical characteristicsof the wood itself (e.g., state of decay, hardness, whether the wood is alive or dead, or thechoice of heartwood versus sapwood versus bark).Many xylophagous insects have symbiotic protozoa and/or bacteria in their digestivesystem which assist in the breakdown of cellulose, others (e.g., the termite familyTermitidae) possess their own cellulase. Others, especially among the groups feeding ondecaying wood, apparently derive much of their nutrition from the digestion of variousfungi that are growing amidst the wood fibers. Such insects often carry the spores of thefungi in special structures on their bodies (called "mycangia"), and infect the host treethemselves when they are laying their eggs.Examples of wood-eating animals • Bark beetles • Giant Panda • Horntails • Termites • Panaque (catfish) • Gribbles • ShipwormsReferences 1. ^ Xulophagos, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at PerseusPlant anatomy, From Wikipedia, the free encyclopedia 215
  • 216. Feeding behaviour of Animals Hematophagy · Insectivore · Lepidophagy · Man-eater · Molluscivore · adult Mucophagy · Ophiophagy · Piscivore · Spongivore Carnivores Oophagy · Ovophagy · Paedophagy · reproductive Placentophagy Autophagy · Cannibalism · Human cannibalistic cannibalism · Self-cannibalism · Sexual cannibalism Folivore · Frugivore · Graminivore · Granivore · Herbivores Nectarivore · Palynivore · Xylophagy Bacterivore · Coprophagia · Detritivore · Fungivore · Others Geophagy · Omnivore Apex predator · Bottom feeding · Hypercarnivore · Filter Methods feeding · Grazing · Kleptoparasitism · Scavenging · Trophallaxis Predation · Carnivorous plant · Carnivorous fungus · Carnivorous protist · Category:Eating behaviors This ecology-related article is a stub. You can help Wikipedia by expanding it.Retrieved from "http://en.wikipedia.org/wiki/Xylophagy"Branch collarA branch collar is the attachment structure in woody plants that connects a branch to itsparent branch or to the trunk. The branch collar consists of overlapping wood fibers.During plant growth cycles, wood on smaller branches forms first. Wood at the base ofthe branch extends slightly over the face of the trunk, forming the branch collar. Then,the wood of the parent branch forms over the top of the basal branch wood, usuallyforming a circular structure called the trunk collar. Together, the branch collar and trunkcollar are simply referred to as the branch collar. Branch collars can also be flat orsomewhat recessed into the trunk or parent branch, as in some conifers.The accretion of layers of wood behind the branch collar is a conical decay-resistantstructure called the branch core. The knot found in lumber is this branch core.When woody plants naturally shed branches because they are nonproductive, usuallyfrom lack of light, these branches die back to the branch collar. Insects and fungidecompose the dead branch, and it eventually falls off, leaving the exposed branch core.Plant anatomy, From Wikipedia, the free encyclopedia 216
  • 217. The branch core resists the spread of decay organisms into the parent branch or trunkduring the time new wood increment growth seals over the wound.Events such as storms or pruning may damage the branch collar, thus defeating thenaturally-occurring defense of the branch core and exposing the trunk to decay.Understanding the branch collar anatomy is important in tree pruning. Pruning practicesthat mimic natural branch shedding avoid unnecessary damage to the plants defensiveanatomy.References • Tree Pruning a Worldwide Photo Guide, Pages 18,19,151 Shigo, Alex L., 1989 for the definitive illustration of a branch collar. ISBN 0943563089See also • Alex Shigo • Tree • Arboriculture • Plant morphologyExternal linksTree pruning guide prepared by the US Forest Service for the US Department ofAgriculture features a diagram of the branch collar.Alex Shigo Alex Shigo (far right) explaining markings on an Oak section during one of his last symposia. Alex Shigo is widely considered the father of modern arboriculture. He developed many of the principles that have become central to arboriculture, and his work served as a foundation for much of the research following it. Shigo was born in Duquesne, Pennsylvania on May 8, 1930. He received his bachelors ofscience from Waynesburg College, near his hometown. After serving in the Korean Warin the Air Force, Shigo returned to his studies at West Virginia University, where hereceived his Masters and PhD.Dr. Shigo spent most of his professional career with the United States Forest Service.Early in his career, the first one-man chainsaws were invented, which allowed Shigo tolook at trees in a way no one else ever had: by making longitudinal cuts (along the stem)rather than transverse cuts (across the stem). This technique led to many importantdiscoveries, many of which were incorporated into CODIT (Compartmentalization ofDecay in Trees), a groundbreaking biological idea that led to many changes and additionsto commercial tree care practices. Shigo eventually became Chief Scientist for the ForestService.From 1985 to 2005, he and his wife Marilyn published books as Shigo and Trees,Associates. In 2005, they transferred ownership of the company to their daughter JudyShigo Smith. Dr. Shigo was well known for his digressive and philosophical style whenPlant anatomy, From Wikipedia, the free encyclopedia 217
  • 218. writing and speaking, and his trademarked phrase, “touch trees,” with which heautographed his books.Dr. Shigo authored over 270 publications, including many research papers, books,pamphlets, CDs, and DVDs. In recent years, Dr. Shigo reduced his travel schedule butcontinued to teach and lead workshop sessions until his untimely death. Dr. Shigo and hiswife Marilyn have a daughter, Judy, and a son, Robert, as well as five grandchildren.Dr. Alex Shigo died on October 6, 2006 at his home in Barrington, New Hampshire. Amemorial service was held on October 11, 2006 in Barrington, at which many arboristsspoke about his influence on their lives and the field of arboriculture.Results of ResearchDr. Shigos discoveries went against many arboricultural conventions that existed prior tohis research. Many techniques that were staples of arboriculture for hundreds or eventhousands of years were shown to be unnecessary or harmful. It took many years, butShigos conclusions have been confirmed by other researchers, and a wealth ofdiscoveries are now built upon his initial work. Current ANSI standards for tree pruningreflect his recommendations.However, many commercial arborists continue to perform flush cuts, toppings, and otherpractices that Dr. Shigos research shows to be harmful. Some of these arborists do notbelieve that Shigos conclusions are accurate. More often, arborists perform thesepractices knowing they are harmful, but believing their business cannot survive withoutdoing so. Although the results of Dr. Shigos research has reached educational andresearch-oriented publications, many consumer-oriented publications still recommend orat least describe pruning and cultural practices that have been shown to be detrimental.References • Shigo, Alex. A New Tree Biology. Shigo and Trees, Associates. ISBN 0-943563- 12-7 • Shigo, Alex. Modern Arboriculture. Shigo and Trees, Associates. ISBN 0- 943563-09-7 • ANSI A300-2001 • Close-Up Profile: Alex Shigo • Shigo and Trees, Official Website Tree For other uses, see Tree (disambiguation). The coniferous Coast Redwood is the tallest tree species on earth. Trunk base of a Coast Redwood tree in Jedediah Smith Redwoods State Park: Simpson Reed Discovery Trail,Plant anatomy, From Wikipedia, the free encyclopedia 218
  • 219. near Crescent City, California A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance.[1] A minimum height specification at maturity is cited by some authors, varying from 3 m[2] to 6 m;[3] some authors set a minimum of 10 cm trunk diameter (30 cm girth).[4] Woody plants that do not meet these definitions by having multiple stems and/or small size, are called shrubs. Comparedwith most other plants, trees are long-lived, some reaching several thousand years old andgrowing to up to 115 m (375 ft) high.[5]Trees are an important component of the natural landscape because of their prevention oferosion and the provision of a weather-sheltered ecosystem in and under their foliage.Trees also play an important role in producing oxygen and reducing carbon dioxide in theatmosphere, as well as moderating ground temperatures. They are also elements inlandscaping and agriculture, both for their aesthetic appeal and their orchard crops (suchas apples). Wood from trees is a building material, as well as an energy source in thirdworld countries. Trees also play a role in many of the worlds mythologies (see trees inmythology).Contents • 1 Classification • 2 Morphology • 3 Record breaking trees o 3.1 Tallest trees o 3.2 Stoutest trees o 3.3 Largest trees o 3.4 Oldest trees • 4 Trees in culture • 5 See also • 6 References • 7 Bibliography • 8 External linksClassificationA Sweet Chestnut tree in Ticino, SwitzerlandPlant anatomy, From Wikipedia, the free encyclopedia 219
  • 220. A tree is a plant form that occurs in many different orders and families of plants. Treesshow a variety of growth forms, leaf type and shape, bark characteristics, andreproductive organs.The tree form has evolved separately in unrelated classes of plants, in response to similarenvironmental challenges, making it a classic example of parallel evolution. With anestimate of 100,000 tree species, the number of tree species worldwide might total 25percent of all living plant species.[6] The majority of tree species grow in tropical regionsof the world and many of these areas have not been surveyed yet by botanists, makingspecies diversity and ranges poorly understood.[7]The earliest trees were tree ferns and horsetails, which grew in forests in theCarboniferous Period; tree ferns still survive, but the only surviving horsetails are not oftree form. Later, in the Triassic Period, conifers, ginkgos, cycads and other gymnospermsappeared, and subsequently flowering plants in the Cretaceous Period. Most species oftrees today are flowering plants (Angiosperms) and conifers. The listing below givesexamples of well-known trees and how they are classified.A small group of trees growing together is called a grove or copse, and a landscapecovered by a dense growth of trees is called a forest. Several biotopes are defined largelyby the trees that inhabit them; examples are rainforest and taiga (see ecozones). Alandscape of trees scattered or spaced across grassland (usually grazed or burned overperiodically) is called a savanna. A forest of great age is called old growth forest orancient woodland (in the UK). A young tree is called a sapling.MorphologyBeech leaves.Plant anatomy, From Wikipedia, the free encyclopedia 220
  • 221. Tree roots anchor the structure and provide water and nutrients. The ground has erodedaway around the roots of this young pine tree.The parts of a tree are the roots, trunk(s), branches, twigs and leaves. Tree stems consistmainly of support and transport tissues (xylem and phloem). Wood consists of xylemcells, and bark is made of phloem and other tissues external to the vascular cambium.Trees may be grouped into exogenous and endogenous trees according to the way inwhich their stem diameter increases. Exogenous trees, which comprise the great majorityof trees (all conifers, and almost all broadleaf trees), grow by the addition of new woodoutwards, immediately under the bark. Endogenous trees, mainly in the monocotyledons(e.g., palms and dragon trees), but also cacti, grow by addition of new material inwards.As an exogenous tree grows, it creates growth rings as new wood is laid downconcentrically over the old wood. In species growing in areas with seasonal climatechanges, wood growth produced at different times of the year may be visible asalternating light and dark, or soft and hard, rings of wood.[3] In temperate climates, andtropical climates with a single wet-dry season alternation, the growth rings are annual,each pair of light and dark rings being one year of growth; these are known as annualrings. In areas with two wet and dry seasons each year, there may be two pairs of lightand dark rings each year; and in some (mainly semi-desert regions with irregular rainfall),there may be a new growth ring with each rainfall.[8] In tropical rainforest regions withconstant year-round climate, growth is continuous and the growth rings are not visiblewith no change in the wood texture. In species with annual rings, these rings can becounted to determine the age of the tree, and used to date cores or even wood taken fromtrees in the past, a practice is known as the science of dendrochronology. Very fewtropical trees can be accurately aged in this manner. Age determination is also impossiblein endogenous trees.The roots of a tree are generally embedded in earth, providing anchorage for the above-ground biomass and absorbing water and nutrients from the soil. It should be noted,however, that while ground nutrients are essential to a trees growth the majority of itsbiomass comes from carbon dioxide absorbed from the atmosphere (see photosynthesis).Above ground, the trunk gives height to the leaf-bearing branches, aiding in competitionwith other plant species for sunlight. In many trees, the arrangement of the branchesoptimizes exposure of the leaves to sunlight.Not all trees have all the plant organs or parts mentioned above. For example, most palmtrees are not branched, the saguaro cactus of North America has no functional leaves, treeferns do not produce bark, etc. Based on their general shape and size, all of these arenonetheless generally regarded as trees. A plant form that is similar to a tree, butgenerally having smaller, multiple trunks and/or branches that arise near the ground, iscalled a shrub. However, no precise differentiation between shrubs and trees is possible.Given their small size, bonsai plants would not technically be trees, but one should notconfuse reference to the form of a species with the size or shape of individual specimens.A spruce seedling does not fit the definition of a tree, but all spruces are trees.Record breaking treesThe worlds champion trees can be rated on height, trunk diameter or girth, total size, andage. It is significant that in each case, the top position is always held by a conifer, thoughPlant anatomy, From Wikipedia, the free encyclopedia 221
  • 222. a different species in each case; in most measures, the second to fourth places are alsoheld by conifers.Tallest treesThe heights of the tallest trees in the world have been the subject of considerable disputeand much exaggeration. Modern verified measurement with laser rangefinders combinedwith tape drop measurements made by tree climbers, carried out by the U.S. EasternNative Tree Society has shown that most older measuring methods and measurements areunreliable, often producing exaggerations of 5% to 15% above the real height. Historicalclaims of trees of 117 m (384 ft), 130 m (427 ft), and even 150 m (492 ft), are nowlargely disregarded as unreliable, fantasy or outright fraud (however, see "Tallestspecimens" chapter in Eucalyptus regnans article). The following are now accepted as thetop five tallest reliably measured species: 1. Coast Redwood (Sequoia sempervirens): 115.55 m (379.1 ft), Redwood National Park, California, United States[9] 2. Coast Douglas-fir (Pseudotsuga menziesii): 99.4 m (326.1 ft), Brummit Creek, Coos County, Oregon, United States[10] 3. Australian Mountain-ash (Eucalyptus regnans): 97.0 m (318.2 ft), Styx Valley, Tasmania, Australia[11] 4. Sitka Spruce (Picea sitchensis): 96.7 m (317.3 ft), Prairie Creek Redwoods State Park, California, United States[12] 5. Giant Sequoia (Sequoiadendron giganteum): 94.9 m (311.4 ft), Redwood Mountain Grove, Kings Canyon National Park, California, United States[13]A view of a tree from below; this may exaggerate apparent heightStoutest treesThe girth of a tree is much easier to measure than the height, as it is a simple matter ofstretching a tape round the trunk, and pulling it taut to find the circumference. Despitethis, UK tree author Alan Mitchell made the following comment about measurements ofyew trees:Plant anatomy, From Wikipedia, the free encyclopedia 222
  • 223. The aberrations of past measurements of yews are beyond belief. For “ example, the tree at Tisbury has a well-defined, clean, if irregular bole at least 1.5 m long. It has been found to have a girth which has dilated and shrunk in the following way: 11.28 m (1834 Loudon), 9.3 m (1892 Lowe), 10.67 m (1903 Elwes and Henry), 9.0 m (1924 E. Swanton), 9.45 m (1959 Mitchell) .... Earlier measurements have therefore been omitted." ”—Alan Mitchell; in a handbook "Conifers in the British Isles".[14] As a general standard, tree girth is taken at breast height; this is defined differently in different situations, with most forestry measurements taking girth at 1.3 m above ground,[15] while those who measure ornamental trees usually measure at 1.5 m above ground;[3] in most cases this makes little difference to the measured girth. On sloping ground, the "above ground" reference point is usually taken as the highest point on the ground touching the trunk,[3][15] but some use the average between the highest and lowest points of ground[citation needed]. Some of the inflated old measurements may have been taken at ground level. Some past exaggerated measurements also result from measuring the complete next-to-bark measurement, pushing the tape in and out over every crevice and buttress.[14] Modern trends are to cite the trees diameter rather than the circumference; this is obtained by dividing the measured circumference by π; it assumes the trunk is circular in cross-section (an oval or irregular cross-section would result in a mean diameter slightly greater than the assumed circle). This is cited as dbh (diameter at breast height) in tree and forestry literature.[3][15] One further problem with measuring baobabs Adansonia is that these trees store large amounts of water in the very soft wood in their trunks. This leads to marked variation in their girth over the year, swelling to a maximum at the end of the rainy season, minimum at the end of the dry season. Although baobabs have some of the highest girth measurements of any trees, no accurate measurements are available, but probably do not exceed 10-11 m (33–36 ft) diameter. The stoutest living single-trunk species in diameter, excluding baobabs, are: 1. Montezuma Cypress Taxodium mucronatum: 11.62 m (38.1 ft), Árbol del Tule, Santa Maria del Tule, Oaxaca, Mexico.[16] Note though that this diameter includes buttressing; the actual idealised diameter of the area of its wood is 9.38 m (30.8 ft).[16] 2. Giant Sequoia Sequoiadendron giganteum: 8.85 m (29 ft), General Grant tree, Grant Grove, California, United States[17] 3. Coast Redwood Sequoia sempervirens: 7.44 m (24.4 ft), Prairie Creek Redwoods State Park, California, United States.[citation needed] Charles Darwin reported finding Fitzroya cupressoides with trunk circumferences of up to 40 m (130 ft)[18] implying a diameter of about 12 m (40 ft), but this may be an anomaly as the largest known measurements are about 5 m.[19] An addition problem lies in cases where multiple trunks (whether from an individual tree or multiple trees) grow together. The Sacred Fig is a notable example of this, forming additional trunks by growing adventitious roots down from the branches, which then thicken up when the root reaches the ground to form new trunks; a single Sacred Fig tree can have hundreds of such trunks.[1] Plant anatomy, From Wikipedia, the free encyclopedia 223
  • 224. Occasionally, errors may occur due to confusion between girth (circumference) anddiameter.[20]Largest treesThe largest trees in total volume are those which are both tall and of large diameter, andin particular, which hold a large diameter high up the trunk. Measurement is verycomplex, particularly if branch volume is to be included as well as the trunk volume, someasurements have only been made for a small number of trees, and generally only forthe trunk. No attempt has ever been made to include root volume. Measuring standardsvary (for example, Del Norte Titan below, is listed as the largest coastal redwood, but theLost Monarch in Jedediah Smith Redwoods State Park is even larger at over 42,000 cubicfeet).The top four species measured[21] so far are: 1. Giant Sequoia Sequoiadendron giganteum: 1,489 m³ (55,040 cu ft), General Sherman[21] 2. Coast Redwood Sequoia sempervirens: 1,045 m³ (36,890 cu ft), Del Norte Titan tree[21] 3. Western Redcedar Thuja plicata: 500 m³ (17,650 cu ft ), Quinault Lake Redcedar[21] 4. Kauri Agathis australis: circa 400 m³ (15,000 cu ft), Tane Mahuta tree[21] (total volume, including branches, 516.7 m³/18,247 cu ft)[21]However, the Alerce Fitzroya cupressoides, as yet un-measured, may well slot in at thirdor fourth place, and Montezuma Cypress Taxodium mucronatum and other giants are alsolikely to be high in the list. The largest angiosperm tree is a Australian Mountain-ash(Eucalyptus regnans) in Tasmania, known as the Two Towers tree, with a volume of430 m³ (15,185 cu ft).[22]Oldest treesThe oldest trees are determined by growth rings, which can be seen if the tree is cut downor in cores taken from the edge to the center of the tree. Accurate determination is onlypossible for trees which produce growth rings, generally those which occur in seasonalclimates; trees in uniform non-seasonal tropical climates grow continuously and do nothave distinct growth rings. It is also only possible for trees which are solid to the centerof the tree; many very old trees become hollow as the dead heartwood decays away. Forsome of these species, age estimates have been made on the basis of extrapolating currentgrowth rates, but the results are usually little better than guesswork or wild speculation.White (1998)[23] proposes a method of estimating the age of large and veteran trees in theUnited Kingdom through the correlation between a trees stem diameter, growth characterand age.The verified oldest measured ages are: 1. Norway Spruce Picea abies: 9,550 years[24] 2. Baobab "Digitata Adansonia": 6,000 years according to carbon dating [25] 3. Great Basin Bristlecone Pine (Methuselah) Pinus longaeva: 4,844 years[26] 4. Alerce Fitzroya cupressoides: 3,622 years[26] 5. Giant Sequoia Sequoiadendron giganteum: 3,266 years[26] 6. Huon-pine Lagarostrobos franklinii: 2,500 years[26] 7. Rocky Mountains Bristlecone Pine Pinus aristata: 2,435 years[26]Plant anatomy, From Wikipedia, the free encyclopedia 224
  • 225. Other species suspected of reaching exceptional age include European Yew Taxusbaccata (probably over 2,000 years[27][28]) and Western Redcedar Thuja plicata.The oldest reported age for an angiosperm tree is 2293 years for the Sri Maha BodhiSacred Fig (Ficus religiosa) planted in 288 BC at Anuradhapura, Sri Lanka; this is alsothe oldest human-planted tree with a known planting date.Trees in culture Main article: Tree (mythology)The tree has always been a cultural symbol. Common icons are the World tree, forinstance Yggdrasil, and the tree of life. The tree is often used to represent nature or theenvironment itself.See also It has been suggested that Exploding tree be merged into this article or section. (Discuss) • Arboretum • List of famous trees • Arboriculture • List of major tree genera • Arborsculpture • Mother of the Forest • Bonsai • Plantation • Christmas tree • Pooktre • Deforestation • Tree climbing • Dendrology • Tree line • Exploding tree • Trees of the world • Fruit trees • Urban forestry • Woodland managementReferences 1. ^ a b Huxley, A., ed. (1992). New RHS Dictionary of Gardening. Macmillan ISBN 0-333- 47494-5. 2. ^ Rushforth, K. (1999). Trees of Britain and Europe. Collins ISBN 0-00-220013-9. 3. ^ a b c d e Mitchell, A. F. (1974). A Field Guide to the Trees of Britain and Northern Europe. Collins ISBN 0-00-212035-6 4. ^ Utkarsh Ghate. "Field Guide to Indian Trees, introductory chapter: Introduction to Common Indian Trees" (RTF). Retrieved on 2007-07-25. 5. ^ Gymnosperm Database: Sequoia sempervirens 6. ^ "TreeBOL project". Retrieved on 2008-07-11. 7. ^ Friis, Ib, and Henrik Balslev. 2005. Plant diversity and complexity patterns: local, regional, and global dimensions : proceedings of an international symposium held at the Royal Danish Academy of Sciences and Letters in Copenhagen, Denmark, 25-28 May, 2003. Biologiske skrifter, 55. Copenhagen: Royal Danish Academy of Sciences and Letters. pp 57-59. 8. ^ Mirov, N. T. (1967). The Genus Pinus. Ronald Press. 9. ^ "Gymnosperm Database: Sequoia sempervirens". Retrieved on 2007-06-10. “Hyperion, Redwood National Park, CA, 115.55 m” 10. ^ "Gymnosperm Database: Pseudotsuga menziesii". Retrieved on 2007-06-10. “The Brummit Fir: Height 99.4 m, dbh 354 cm, on E. Fork Brummit Creek in Coos County, Oregon; in 1998” 11. ^ "Ten Tallest Trees (of Tasmania)". Tasmanian Giant Trees. Retrieved on 2007-06- 10. “Height (m): 97; Diameter (cm): 290; Volume (m³): 164; Species: E.regnans; TreePlant anatomy, From Wikipedia, the free encyclopedia 225
  • 226. identification: TT326; Name: Icarus Dream; Location: Andromeda; Year last measured: 2005” 12. ^ "Gymnosperm Database: Picea sitchensis". Retrieved on 2007-06-10. “This tree also has a sign nearby proclaiming it to be the worlds largest spruce. The two tallest on record, 96.7 m and 96.4 m, are in Prairie Creek Redwoods State Park, California” 13. ^ "Gymnosperm Database: Sequoiadendron giganteum". Retrieved on 2007-06-10. “The tallest known giant sequoia is a specimen 94.9 m tall, first measured August 1998 in the Redwood Mountain Grove, California” 14. ^ a b Mitchell, A. F. (1972). Conifers in the British Isles. Forestry Commission Booklet 33. 15. ^ a b c Hamilton, G. J. (1975). Forest Mensuration Handbook. Forestry Commission Booklet 39. ISBN 0-11-710023-4. 16. ^ a b Gymnosperm Database: Taxodium mucronatum 17. ^ "Gymnosperm Database: Sequoiadendron giganteum". Retrieved on 2007-06-10. “the General Grant tree in Kings Canyon National Park, CA, which is 885 cm dbh and 81.1 m tall” 18. ^ Gymnosperm Database: Fitzroya 19. ^ Golte, W. (1996). Exploitation and conservation of Fitzroya cupressoides in southern Chile. Pp. 133–150 in: Hunt, D., ed. Temperate Trees under Threat. International Dendrology Society ISBN 0-9504544-6-X. 20. ^ See e.g. the uncertainty over the size of the largest Abies nordmanniana at the Gymnosperm Database: Abies nordmanniana page 21. ^ a b c d e f "Gymnosperm Database: A Tale of Big Tree Hunting In California". Retrieved on 2007-06-10. “Sequoiadendron giganteum is 1489 m³, Sequoia sempervirens 1045 m³, Thuja plicata 500 m³, Agathis australis ca. 400 m³” 22. ^ "Tasmanias ten most massive giants". Tasmanian Giant Trees. Retrieved on 2007-06- 10. “Height (m): 75; Diameter (cm): 580; Volume (m³): 430; Species: E.regnans; Tree identification: TT38; Name:Two Towers; Location: Jacques Road; Year last measured: 2006” 23. ^ White, J. (1990). Estimating the Age of Large and Veteran Trees in Britain. Forestry Commission Edinburgh. 24. ^ Umeå University Press Release: World’s oldest living tree discovered in Sweden. April 16, 2008. 25. ^ [1]. 26. ^ a b c d e Gymnosperm Database: How Old Is That Tree?. Retrieved on 2008-04-17. 27. ^ Harte, J. (1996). How old is that old yew? At the Edge 4: 1-9. Available online 28. ^ Kinmonth, F. (2006). Ageing the yew - no core, no curve? International Dendrology Society Yearbook 2005: 41-46 ISSN 0307-332XBibliography • Pakenham, T. (2002). Remarkable Trees of the World. ISBN 0-297-84300-1 • Pakenham, T. (1996). Meetings with Remarkable Trees. ISBN 0-297-83255-7 • Tudge, C. (2005). The Secret Life of Trees. How They Live and Why They Matter. Allen Lane. London. ISBN 0-713-99698-6External links Wikimedia Commons has media related to: TreesPlant anatomy, From Wikipedia, the free encyclopedia 226
  • 227. Look up tree in Wiktionary, the free dictionary. • Global Trees Campaign (campaigning to save the worlds most threatened trees) • International Society of Arboriculture • The Arbor Day Foundation • Shade and Ornamental Trees for KansasArboriculture Good arboricultural care can reduce the risks of broken tree branches like this oneJames Kinder, an ISA Certified MunicipalArborist examining a Japanese Hemlock atHoyt Arboretum in Portland, Oregon.Arboriculture (pronounced /ɑːbərɪkʌltʃə/) is the cultivation of trees and shrubs. Thediscipline includes the study of how they grow and respond to cultural practices and theenvironment as well as aspects of cultivation such as selection, planting, care, andremoval.The purpose is generally to manage amenity trees. That is trees where their value to thelandscape is greater than that of their wood content. Trees offer environmental benefits aswell as cultural, heritage and habitat for fauna. The combined value including aestheticsexceeds the value of a trees worth from a forestry wood perspective. Amenity trees areusually in a garden or urban setting, and arboriculture is the management of them forplant health and longevity, pest and pathogen resistance, risk management andornamental or aesthetic reasons. In this, it needs to be distinguished from forestry, whichis the commercial production and use of timber and other forest products from plantationsand forests. Some definitions of the term arboriculture extend it only to the care of trees."Arboriculture" is not synonymous with Arborsculpture.See also • Arboring • Arborist • Arborsculpture • Bonsai • Horticulture • International Society of Arboriculture • Landscape architecture • Landscaping • Urban forestry • ViticulturePlant anatomy, From Wikipedia, the free encyclopedia 227
  • 228. External links • ArbWiki.com Wiki dedicated the Aboricultural Industry - Contributors Welcome! • BatsandTrees.com Promoting the importance of British trees to bats • European Arboricultural Council • Institute of Chartered Foresters The Royal Chartered body for forestry and arboricultural professionals in the UK • International Society of Arboriculture (USA) • TreesAreGood.com (arboricultural resources for the general public) • Green Options Tree Care - Portland, Oregon Arboricultural ConsultantsReferences • Harris, Richard W. (1983). ARBORICULTURE: Care of Trees, Shrubs, and Vines in the Landscape. Englewood Cliffs, New Jersey 07632: Prentice-Hall, Inc., pp. 2-3. ISBN 0-13-043935-5. • "arboriculture". Merriam-Websters Collegiate Dictionary, Eleventh Edition http://www.m-w.com/dictionary/arboriculture. Merriam-Webster. Retrieved on 2007-06-08. • "arboriculture". Encyclopædia Britannica Online http://www.britannica.com/eb/article-9009233. (2007). Encyclopaedia Britannica. Retrieved on 2007-06-08. • "arboriculture". The American Heritage Dictionary of the English Language, Fourth Edition Online http://www.bartleby.com/61/4/A0400400.html. (2000). Houghton Mifflin Company. Retrieved on 2007-06-08.Retrieved from "http://en.wikipedia.org/wiki/Arboriculture"Categories: Gardening | Horticulture | ForestryRootFor other uses, see Root (disambiguation).Primary and secondary roots in a cotton plantIn vascular plants, the root is the organ of a plant body that typically lies below thesurface of the soil. But, this is not always the case, since a root can also be aerial (that is,growing above the ground) or aerating (that is, growing up above the ground orespecially above water). On the other hand, a stem normally occurring below ground isnot exceptional either (see rhizome). So, it is better to define root as a part of a plant bodythat bears no leaves, and therefore also lacks nodes. There are also important internalstructural differences between stems and roots. The two major functions of roots are 1.)Plant anatomy, From Wikipedia, the free encyclopedia 228
  • 229. absorption of water and inorganic nutrients and 2.) anchoring the plant body to theground. Roots also function in cytokinin synthesis, which supplies some of the shootsneeds. They often function in storage of food. The roots of most vascular plant speciesenter into symbiosis with certain fungi to form mycorrhizas, and a large range of otherorganisms including bacteria also closely associate with roots.Contents[hide] • 1 Root structure o 1.1 Secondary growth • 2 Root growth • 3 Types of roots o 3.1 Specialized roots • 4 Rooting depths • 5 Root architecture • 6 Economic importance • 7 See also • 8 References • 9 External linksRoot structure Roots of a hydroponically grown plant At the tip of every growing root is a conical covering of tissue called the root cap, which consists of undifferentiated soft tissue (parenchyma) with unthickened walls covering the apical meristem. The root cap provides mechanical protection to the meristem as the root advances through the soil. As the root cap cells are worn away they are continually replaced by new cells generated by cell division within the meristem. The root cap is also involved in the production of mucigel, a sticky mucilage that coats the new formed cells. These cells contain statoliths, starchgrains that move in response to gravity and thus control root orientation.The outside surface of the primary root is the epidermis. Recently produced epidermalcells absorb water from the surrounding environment and produce outgrowths called roothairs that greatly increase the cells absorptive surface. Root hairs are very delicate andgenerally short-lived, remaining functional for only a few days. However, as the rootgrows, new epidermal cells emerge and these form new root hairs, replacing those thatdie. The process by which water is absorbed into the epidermal cells from the soil isknown as osmosis. For this reason, water that is saline is more difficult for most plantspecies to absorb.Beneath the epidermis is the cortex, which comprises the bulk of the primary root. Itsmain function is storage of starch. Intercellular spaces in the cortex aerate cells forrespiration. An endodermis is a thin layer of small cells forming the innermost part ofthe cortex and surrounding the vascular tissues deeper in the root. The tightly packedPlant anatomy, From Wikipedia, the free encyclopedia 229
  • 230. cells of the endodermis contain a substance known as suberin in their cell walls. Thissuberin layer is the Casparian strip, which creates an impermeable barrier of sorts.Mineral nutrients can only move passively within root cell walls until they reach theendodermis. At that point, they must be actively transported across a cell membrane tocontinue further into the root. This allows the plant to accumulate mineral nutrients in thestele.The vascular cylinder, or stele, consists of the cells inside the endodermis. The outer part,known as the pericycle, surrounds the actual vascular tissue. In monocotyledonous plants, the xylem and phloem cells are arranged in a circle around a pith or center, whereas in dicotyledons, the xylem cells form a central "hub" with lobes, and phloem cells fill in the spaces between the lobes. Cross section of the root of a dicotyledonSecondary growthAll roots have primary growth or growthin length. Roots of many vascular plants,especially dicots and gymnosperms, oftenundergo secondary growth, which is anincrease in diameter. A vascular cambiumforms in the stele to produce secondaryphloem and secondary xylem. Theepidermis is replaced by a periderm. Asthe stele increases in diameter, the cortex,pericycle and endodermis are lost. Evennon-woody roots often undergo secondarygrowth, including those of tomato andalfalfa.Root growthRoot systems of prairie plantsPlant anatomy, From Wikipedia, the free encyclopedia 230
  • 231. Cross Section of a mango tree Early root growth is one of the functions of the apical meristem located near the tip of the root. The meristem cells more or less continuously divide, producing more meristem, root cap cells (these sacrificed to protect the meristem), and undifferentiated root cells. The latter will become the primary tissues of the root, first undergoing elongation, a process that pushes the root tipforward in the growing medium. Gradually these cells differentiate and mature intospecialized cells of the root tissues.Roots will generally grow in any direction where the correct environment of air, mineralnutrients and water exists to meet the plants needs. Roots will not grow in dry soil. Overtime, given the right conditions, roots can crack foundations, snap water lines, and liftsidewalks. At germination, roots grow downward due to gravitropism, the growthmechanism of plants that also causes the shoot to grow upward. In some plants (such asivy), the "root" actually clings to walls and structures.Growth from apical meristems is known as primary growth, which encompasses allelongation. Secondary growth encompasses all growth in diameter, a major componentof woody plant tissues and many nonwoody plants. For example, storage roots of sweetpotato have secondary growth but are not woody. Secondary growth occurs at the lateralmeristems, namely the vascular cambium and cork cambium. The former formssecondary xylem and secondary phloem, while the latter forms the periderm.In plants with secondary growth, the vascular cambium, originating between the xylemand the phloem, forms a cylinder of tissue along the stem and root. The cambium layerforms new cells on both the inside and outside of the cambium cylinder, with those on theinside forming secondary xylem cells, and those on the outside forming secondaryphloem cells. As secondary xylem accumulates, the "girth" (lateral dimensions) of thestem and root increases. As a result, tissues beyond the secondary phloem (including theepidermis and cortex, in many cases) tend to be pushed outward and are eventually "sloughed off" (shed). At this point, the cork cambium begins to form the periderm, consisting of protective cork cells containing suberin. In roots, the cork cambium originates in the pericycle, a component of the vascular cylinder. Stilt roots in the Amazon Rainforest support a tree in very soft, wet soil conditionsPlant anatomy, From Wikipedia, the free encyclopedia 231
  • 232. The vascular cambium produces new layers of secondary xylem annually. The xylemvessels are dead at maturity but are responsible for most water transport through thevascular tissue in stems and roots.Types of rootsA true root system consists of a primary root and secondary roots (or lateral roots).The primary root originates in the radicle of the seedling. It is the first part of the root tobe originated. During its growth it rebranches to form the lateral roots. It usually growsdownwards. Generally, two categories are recognized: • the taproot system: the primary root is prominent and has a single, dominant axis; there are fibrous secondary roots running outward. Usually allows for deeper roots capable of reaching low water tables. Most common in dicots. The main function of the taproot is to store food. • the diffuse root system: the primary root is not dominant; the whole root system is fibrous and branches in all directions. Most common in monocots. The main function of the fibrous root is to anchor the plant.Specialized rootsAerating roots of a mangroveButtress roots of Ceiba pentandraThe roots, or parts of roots, of many plant species have become specialized to serveadaptive purposes besides the two primary functions described in the introduction. • Adventitious roots arise out-of-sequence from the more usual root formation of branches of a primary root, and instead originate from the stem, branches, leaves, or old woody roots. They commonly occur in monocots and pteridophytes, but also in many dicots, such as clover (Trifolium), ivy (Hedera), strawberryPlant anatomy, From Wikipedia, the free encyclopedia 232
  • 233. (Fragaria) and willow (Salix). Most aerial roots and stilt roots are adventitious. In some conifers adventitious roots can form the largest part of the root system. • Aerating roots (or pneumatophores): roots rising above the ground, especially above water such as in some mangrove genera (Avicennia, Sonneratia). In some plants like Avicennia the erect roots have a large number of breathing pores for exchange of gases. • Aerial roots: roots entirely above the ground, such as in ivy (Hedera) or in epiphytic orchids. They function as prop roots, as in maize or anchor roots or as the trunk in strangler fig. • Contractile roots: they pull bulbs or corms of monocots, such as hyacinth and lily, and some taproots, such as dandelion, deeper in the soil through expanding radially and contracting longitudinally. They have a wrinkled surface. • Coarse roots: Roots that have undergone secondary thickening and have a woody structure. These roots have some ability to absorb water and nutrients, but their main function is transport and to provide a structure to connect the smaller diameter, fine roots to the rest of the plant. • Fine roots: Primary roots usually <2 mm diameter that have the function of water and nutrient uptake. They are often heavily branched and support mycorrhizas. These roots may be short lived, but are replaced by the plant in an ongoing process of root turnover. • Haustorial roots: roots of parasitic plants that can absorb water and nutrients from another plant, such as in mistletoe (Viscum album) and dodder. • Propagative roots: roots that form adventitious buds that develop into aboveground shoots, termed suckers, which form new plants, as in Canada thistle, cherry and many others. • Proteoid roots or cluster roots: dense clusters of rootlets of limited growth that develop under low phosphate or low iron conditions in Proteaceae and some plants from the following families Betulaceae, Casuarinaceae, Eleagnaceae, Moraceae, Fabaceae and Myricaceae. • Stilt roots: these are adventitious support roots, common among mangroves. They grow down from lateral branches, branching in the soil. • Storage roots: these roots are modified for storage of food or water, such as carrots and beets. They include some taproots and tuberous roots. • Structural roots: large roots that have undergone considerable secondary thickening and provide mechanical support to woody plants and trees. • Surface roots: These proliferate close below the soil surface, exploiting water and easily available nutrients. Where conditions are close to optimum in the surface layers of soil, the growth of surface roots is encouraged and they commonly become the dominant roots. • Tuberous roots: A portion of a root swells for food or water storage, e.g. sweet potato. A type of storage root distinct from taproot.Plant anatomy, From Wikipedia, the free encyclopedia 233
  • 234. Roots from a fallen redwood at Yosemite National Park.Rooting depthsThe distribution of vascular plant roots within soil depends on plant form, the spatial andtemporal availability of water and nutrients, and the physical properties of the soil. Thedeepest roots are generally found in deserts and temperate coniferous forests; theshallowest in tundra, boreal forest and temperate grasslands. The deepest observed livingroot, at least 60 m below the ground surface, was observed during the excavation of anopen-pit mine in Arizona, USA. Some roots can grow as deep as the tree is high. Themajority of roots on most plants are however found relatively close to the surface wherenutrient availability and aeration are more favourable for growth. Rooting depth may bephysically restricted by rock or compacted soil close below the surface, or by anaerobicsoil conditions.Root architectureThe pattern of development of a root system is termed root architecture, and is importantin providing a plant with a secure supply of nutrients and water as well as anchorage andsupport. The architecture of a root system can be considered in a similar way to above-ground architecture of a plant - i.e. in terms of the size, branching and distribution of thecomponent parts. In roots, the architecture of fine roots and coarse roots can both bedescribed by variation in topology and distribution of biomass within and between roots.Having a balanced architecture allows fine roots to exploit soil efficiently around a plant,but the plastic nature of root growth allows the plant to then concentrate its resourceswhere nutrients and water are more easily available. A balanced coarse root architecture,Plant anatomy, From Wikipedia, the free encyclopedia 234
  • 235. with roots distributed relatively evenly around the stem base, is necessary to providesupport to larger plants and trees.Economic importanceRoots can also protect the environment by holding the soil to prevent soil erosionTree roots at Cliffs of the Neuse State Park, NCThe term root crops refers to any edible underground plant structure, but many root cropsare actually stems, such as potato tubers. Edible roots include cassava, sweet potato, beet,carrot, rutabaga, turnip, parsnip, radish, yam and horseradish. Spices obtained from rootsinclude sassafras, angelica, sarsaparilla and licorice.Sugar beet is an important source of sugar. Yam roots are a source of estrogencompounds used in birth control pills. The fish poison and insecticide rotenone isobtained from roots of Lonchocarpus spp. Important medicines from roots are ginseng,aconite, ipecac, gentian and reserpine. Several legumes that have nitrogen-fixing rootnodules are used as green manure crops, which provide nitrogen fertilizer for other cropswhen plowed under. Specialized bald cypress roots, termed knees, are sold as souvenirs,lamp bases and carved into folk art. Native Americans used the flexible roots of whitespruce for basketry.Tree roots can heave and destroy concrete sidewalks and crush or clog buried pipes. Theaerial roots of strangler fig have damaged ancient Mayan temples in Central America andthe temple of Angkor Wat in Cambodia.Vegetative propagation of plants via cuttings depends on adventitious root formation.Hundreds of millions of plants are propagated via cuttings annually includingchrysanthemum, poinsettia, carnation, ornamental shrubs and many houseplants.Roots can also protect the environment by holding the soil to prevent soil erosion.See also • Rooting Powder • Fibrous root system • Mycorrhiza - root symbiosis in which individual hyphae extending from the mycelium of a fungus colonize the roots of a host plant.Plant anatomy, From Wikipedia, the free encyclopedia 235
  • 236. • Rhizosphere (ecology) - region of soil around the root influenced by root secretions and microorganisms present • Root cutting • StolonReferences • Brundrett, M. C. 2002. Coevolution of roots and mycorrhizas of land plants. New phytologist 154(2): 275-304. (Available online: DOI | Abstract | Full text (HTML) | Full text (PDF)) • Chen, R., E. Rosen, P. H. Masson. 1999. Gravitropism in Higher Plants. Plant Physiology 120 (2): 343-350. (Available online: Full text (HTML) | Full text (PDF)) - article about how the roots sense gravity. • Clark, Lynn. 2004. Primary Root Structure and Development - lecture notes • Coutts, M.P. 1987. Developmental processes in tree root systems. Canadian Journal of Forest Research 17: 761-767. • Raven, J. A., D. Edwards. 2001. Roots: evolutionary origins and biogeochemical significance. Journal of Experimental Botany 52 (Suppl 1): 381-401. (Available online: Abstract | Full text (HTML) | Full text (PDF)) • Schenk, H.J., and R.B. Jackson. 2002. The global biogeography of roots. Ecological Monographs 72 (3): 311-328. • Sutton, R.F., and R.W. Tinus. 1983. Root and root system terminology. Forest Science Monograph 24 pp 137. • Phillips, W.S. 1963. Depth of roots in soil. Ecology 44 (2): 424.External links Wikimedia Commons has media related to: RootsAuxinIAA appears to be the most active auxin in plant growth.Auxins are a class of plant growth substance (often called phytohormone or planthormone). Auxins play an essential role in coordination of many growth and behavioralprocesses in the plant life cycle.Plant anatomy, From Wikipedia, the free encyclopedia 236
  • 237. Contents • 1 Overview • 2 Hormonal activity o 2.1 Molecular mechanisms o 2.2 On a cellular level o 2.3 Organ patterns o 2.4 Organization of the plant • 3 Locations • 4 Effects o 4.1 Wounding response o 4.2 Root growth and development o 4.3 Apical dominance o 4.4 Ethylene biosynthesis o 4.5 Fruit growth o 4.6 Flowering • 5 Herbicide manufacture • 6 See also • 7 ReferencesOverviewAuxins derive their name from the Greek word auxano (to grow). They were the first ofthe major plant hormones to be discovered and are a major coordinating signal in plantdevelopment. Their pattern of active transport through the plant is complex. Theytypically act in concert with (or opposition to) other plant hormones. For example, theratio of auxin to cytokinin in certain plant tissues determines initiation of root versusshoot buds. Thus a plant can (as a whole) react on external conditions and adjust to them,without requiring a nervous system. On a molecular level, auxins have an aromatic ringand a carboxylic acid group (Taiz and Zeiger, 1998).The most important member of the auxin family is indole-3-acetic acid (IAA). Itgenerates the majority of auxin effects in intact plants, and is the most potent nativeauxin. However, molecules of IAA are chemically labile in aqueous solution, so IAA isnot used commercially as a plant growth regulator. • Naturally-occurring auxins include 4-chloro-indoleacetic acid, phenylacetic acid (PAA) and indole-3-butyric acid (IBA). • Synthetic auxin analogs include 1-naphthaleneacetic acid (NAA), 2,4- dichlorophenoxyacetic acid (2,4-D), and others.Gallery of native auxins Indole-3-butyric acid 2-phenylacetic acidindole-3-acetic acid(IBA) 4-chloroindole-3-acetic (PAA)(IAA) acid (4-CI-IAA)Plant anatomy, From Wikipedia, the free encyclopedia 237
  • 238. Gallery of synthetic auxins2,4- 4-Amino-3,5,6-Dichlorophenoxyacetic trichloropicolinic α-Naphthalene acetic acid2-Methoxy-3,6-acid (2,4-D) dichlorobenzoic acid (tordon or (α-NAA) acid (dicamba) picloram)2,4,5-Trichlorophenoxyacetic α-(p-acid (2,4,5-T) Chlorophenoxy)isobutyric acid (PCIB, an antiauxin)Auxins are often used to promote initiation of adventitious roots and are the activeingredient of the commercial preparations used in horticulture to root stem cuttings. Theycan also be used to promote uniform flowering, to promote fruit set, and to preventpremature fruit drop.Used in high doses, auxin stimulates the production of ethylene. Excess ethylene caninhibit elongation growth, cause leaves to fall (leaf abscission), and even kill the plant.Some synthetic auxins such as 2,4-D and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)have been used as herbicides. Broad-leaf plants (dicots) such as dandelions are muchmore susceptible to auxins than narrow-leaf plants (monocots) like grass and cereal crops. These synthetic auxins were the active agents in Agent Orange, a defoliant used extensively by American forces in the Vietnam War. Hormonal activity Auxins coordinate development at all levels in plants, from the cellular level to organs and ultimately the whole plant. The plant cell wall isPlant anatomy, From Wikipedia, the free encyclopedia 238
  • 239. made up of cellulose, protein, and, in many cases, lignin. It is very firm and prevents anysudden expansion of cell volume, and, without contribution of auxins, any expansion atall.Molecular mechanismsAuxins directly stimulate or inhibit the expression of specific genes. Auxin inducestranscription by targeting for degradation members of the Aux/IAA family oftranscriptional repressor proteins, The degradation of the Aux/IAAs leads to thederepression of Auxin Respose Factors ARF-mediated transcription. Aux/IAAs aretargeted for degradation by ubiquitination, catalysed by an SCF-type ubiquitin-proteinligase.In 2005, it was demonstrated that the F-box protein TIR1, which is part of the ubiquitinligase complex SCFTIR1, is an auxin receptor. Upon auxin binding TIR1 recruits specifictranscriptional repressors (the Aux/IAA repressors) for ubiquitination by the SCFcomplex. This marking process leads to the degradation of the repressors by theproteasome, alleviating repression and leading to specific gene expression in response toauxins (reviewed in [1]).Another protein called ABP1 (Auxin Binding Protein 1) is a putative receptor, but its roleis unclear. Electrophysiological experiments with protoplasts and anti-ABP1 antibodiessuggest that ABP1 may have a function at the plasma membrane.On a cellular level This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unverifiable material may be challenged and removed. (June 2008)On the cellular level, auxin is essential for cell growth, affecting both cell division andcellular expansion. Depending on the specific tissue, auxin may promote axial elongation(as in shoots), lateral expansion (as in root swelling), or isodiametric expansion (as infruit growth). In some cases (coleoptile growth) auxin-promoted cellular expansionoccurs in the absence of cell division. In other cases, auxin-promoted cell division andcell expansion may be closely sequenced within the same tissue (root initiation, fruitgrowth). In a living plant it appears that auxins and other plant hormones nearly alwaysinteract to determine patterns of plant development.According to the acid growth hypothesis for auxin action, auxins may directly stimulatethe early phases of cell elongation by causing responsive cells to actively transporthydrogen ions out of the cell, thus lowering the pH around cells. This acidification of thecell wall region activates wall-loosening proteins known as expansins, which allowslippage of cellulose microfibrils in the cell wall, making the cell wall less rigid. Whenthe cell wall is loosened by the action of auxins, this now-less-rigid wall is expanded bycell turgor pressure, which presses against the cell wall.[citation needed]However, the acid growth hypothesis does not by itself account for the increasedsynthesis and transport of cell wall precursors and secretory activity in the Golgi systemthat accompany and sustain auxin-promoted cell expansion.[citation needed]Organ patternsGrowth and division of plant cells together result in growth of tissue, and specific tissuegrowth contributes to the development of plant organs. Growth of cells contributes to theplants size, but uneven localized growth produces bending, turning and directionalizationPlant anatomy, From Wikipedia, the free encyclopedia 239
  • 240. of organs- for example, stems turning toward light sources (phototropism), roots growingin response to gravity (gravitropism), and other tropisms.Organization of the plantAs auxins contribute to organ shaping, they are also fundamentally required for properdevelopment of the plant itself. Without hormonal regulation and organization, plantswould be merely proliferating heaps of similar cells. Auxin employment begins in theembryo of the plant, where directional distribution of auxin ushers in subsequent growthand development of primary growth poles, then forms buds of future organs. Throughoutthe plants life, auxin helps the plant maintain the polarity of growth and recognize whereit has its branches (or any organ) connected.An important principle of plant organization based upon auxin distribution is apicaldominance, which means that the auxin produced by the apical bud (or growing tip)diffuses downwards and inhibits the development of ulterior lateral bud growth, whichwould otherwise compete with the apical tip for light and nutrients. Removing the apicaltip and its suppressive hormone allows the lower dormant lateral buds to develop, and thebuds between the leaf stalk and stem produce new shoots which compete to become thelead growth. This behavior is used in pruning by horticulturists.Uneven distribution of auxin: To cause growth in the required domains, it is necessarythat auxins be active preferentially in them. Auxins are not synthesized everywhere, buteach cell retains the potential ability to do so, and only under specific conditions willauxin synthesis be activated. For that purpose, not only do auxins have to be translocatedtoward those sites where they are needed but there has to be an established mechanism todetect those sites. Translocation is driven throughout the plant body primarily from peaksof shoots to peaks of roots. For long distances, relocation occurs via the stream of fluid inphloem vessels, but, for short-distance transport, a unique system of coordinated polartransport directly from cell to cell is exploited. This process of polar auxin transport isdirectional and very strictly regulated. It is based in uneven distribution of auxin effluxcarriers on the plasma membrane, which send auxins in the proper direction.A 2006 study showed plant-specific pin-formed (PIN) proteins are vital in transportingauxin. PINs also regulate auxin efflux from mammalian and yeast cells.[2]Locations • In shoot (and root) meristematic tissue • In young leaves • In mature leaves in very tiny amounts • In mature root cells in even smaller amounts • Transported throughout the plant more prominently downward from the shoot apicesPlant anatomy, From Wikipedia, the free encyclopedia 240
  • 241. EffectsA healthy Arabidopsis thaliana plant (left) next to an auxin signal-transduction mutantCrown galls are caused by Agrobacterium tumefaciens bacteria; they produce and excreteauxin and cytokinin, which interfere with normal cell division and cause tumorsThe plant hormone stimulates cell elongation. It stimulates the Wall Loosening Factors,for example, elastins, to loosen the cell walls. If gibberellins are also present, the effect isstronger. It also stimulates cell division if cytokinins are present. When auxin andcytokinin are applied to callus, rooting can be generated if the auxin concentration ishigher than cytokinin concentration while xylem tissues can be generated when the auxinconcentration is equal to the cytokinins.It participates in phototropism, geotropism, hydrotropism and other developmentalchanges. The uneven distribution of auxin, due to environmental cues (for example,unidirectional light and gravity force), results in uneven plant tissue growth.It also induces sugar and mineral accumulation at the site of application.Plant anatomy, From Wikipedia, the free encyclopedia 241
  • 242. Wounding responseIt induces formation and organization of phloem and xylem. When the plant is wounded,the auxin may induce the Cell differentiation and regeneration of the vascular tissues.Root growth and developmentAuxin induces new root formation by breaking root apical dominance induced bycytokinins. In horticulture, auxins, especially NAA and IBA, are commonly applied tostimulate root growth when taking cuttings of plants. However, high concentrations ofauxin inhibit root elongation and instead enhance adventitious root formation. Removalof the root tip can lead to inhibition of secondary root formation.Apical dominanceIt induces shoot apical dominance; the axillary buds are inhibited by auxin. When theapex of the plant is removed, the inhibitory effect is removed and the growth of lateralbuds is enhanced as a high concentration of auxin directly stimulates ethylene synthesisin lateral buds causes inhibition of its growth and potentiation of apical dominance.Ethylene biosynthesisIn low concentrations, auxin can inhibit ethylene formation and transport of precursor inplants; however, high concentrations of auxin can induce the synthesis of ethylene.Therefore, the high concentration can induce femaleness of flowers in some species.[citationneeded]It inhibits abscission prior to formation of abscission layer and thus inhibits senescence ofleaves.Fruit growthAuxin delays fruit senescence.It is required for fruit growth. When seeds are removed from strawberries, fruit growth isstopped; exogenous auxin stimulates the growth in seed removed fruits. For fruit withunfertilized seeds, exogenous auxin results in parthenocarpy ("virgin-fruit" growth).FloweringAuxin plays a minor role in the initiation of flowering. It can delay the senescence offlowers in low concentrations.Herbicide manufactureThe defoliant Agent Orange was a mix of 2,4-D and 2,4,5-T. The compound 2,4-D is stillin use and is thought to be safe, but 2,4,5-T was more or less banned by the EPA in 1979.The dioxin TCDD is an unavoidable contaminant produced in the manufacture of 2,4,5-T. As a result of the integral dioxin contamination, 2,4,5-T has been implicated inleukaemia, miscarriages, birth defects, liver damage, and other diseases. Agent Orangewas sprayed in Vietnam as a defoliant to deny ground cover to the Vietnamese army.See also • Herbicide • Pruning fruit trees • FusicoccinReferences • Plant Physiology Online - Chapter 19: Auxin: The Growth Hormone • Plant PhysiologyTaiz, L. & Zeiger, E. (1998). Plant Physiology. 2nd edition. Massachusetts: SinauerAssociates, Inc. 792 p.Plant anatomy, From Wikipedia, the free encyclopedia 242
  • 243. Fibrous root systemA fibrous root system (sometimes also called adventitious root system) is the oppositeof a taproot system. It is usually formed by thin, moderately branching roots growingfrom the stem. A fibrous root system is universal in monocotyledonous plants and ferns,and is also common in dicotyledonous plants.Most trees begin life with a taproot, but after one to a few years change to a wide-spreading fibrous root system with mainly horizontal surface roots and only a fewvertical, deep anchoring roots. A typical mature tree 30-50 m tall has a root system thatextends horizontally in all directions as far as the tree is tall or more, but well over 95%of the roots are in the top 50 cm depth of soil.A few plants with fibrous root systems: [1] • Coconut palm • Gabrielles • Pteridophyta • White clover (Trifolium repens) • MarigoldWeeds that have fibrous root systems can be hard to pull from the ground. Pulled weedsmay grow back from any roots that were left in the soil.References 1. ^ P.K. Thampan. 1981. Handbook on Coconut Palm. Oxford & IBH Publishing Co.External links • Ohio State site This botany article is a stub. You can help Wikipedia by expanding it.MycorrhizaA mycorrhiza (Greek for fungus roots coined by Frank, 1885[1]; typically seen in theplural forms mycorrhizae or mycorrhizas) is a symbiotic (occasionally weaklypathogenic) association between a fungus and the roots of a plant.[2] In a mycorrhizalassociation the fungus may colonize the roots of a host plant either intracellularly orextracellularly.This mutualistic association provides the fungus with relatively constant and direct accessto mono- or dimeric carbohydrates, such as glucose and sucrose produced by the plant inphotosynthesis.[3] The carbohydrates are translocated from their source location (usuallyleaves) to the root tissues and then to the fungal partners. In return, the plant gains the useof the myceliums very large surface area to absorb water and mineral nutrients from thesoil, thus improving the mineral absorption capabilities of the plant roots.[4] Plant rootsalone may be incapable of taking up phosphate ions that are immobilized, for example, insoils with a basic pH. The mycelium of the mycorrhizal fungus can however access thesephosphorus sources, and make them available to the plants they colonize.[5] Themechanisms of increased absorption are both physical and chemical. Mycorrhizalmycelia are much smaller in diameter than the smallest root, and can explore a greatervolume of soil, providing a larger surface area for absorption. Also, the cell membranePlant anatomy, From Wikipedia, the free encyclopedia 243
  • 244. chemistry of fungi is different from that of plants. Mycorrhizae are especially beneficialfor the plant partner in nutrient-poor soils.Mycorrhizal plants are often more resistant to diseases, such as those caused by microbialsoil-borne pathogens, and are also more resistant to the effects of drought. These effectsare perhaps due to the improved water and mineral uptake in mycorrhizal plants.Mycorrhizae form a mutualistic relationship with the roots of most plant species(although only a small proportion of all species have been examined, 95% of all plantfamilies are predominantly mycorrhizal).[6]Plants grown in sterile soils and growth media often perform poorly without the additionof spores or hyphae of mycorrhizal fungi to colonise the plant roots and aid in the uptakeof soil mineral nutrients. The absence of mycorrhizal fungi can also slow plant growth inearly succession or on degraded landscapes.[7]Contents • 1 Occurrence of mycorrhizal associations • 2 Types of mycorrhiza o 2.1 Endomycorrhiza o 2.2 Ectomycorrhiza • 3 See also • 4 References • 5 External linksOccurrence of mycorrhizal associationsAt around 400 million years old, the Rhynie chert contains the earliest fossil assemblageyielding plants preserved in sufficient detail to detect mycorrhizae - and they are indeedobserved in the stems of Aglaophyton major.[8]Mycorrhizae are present in 92% of plant families (80% of species)[9], with arbuscularmycorrhizae being the ancestral and predominant form,[9] and indeed the most prevalentsymbiotic association found in plants at all.[3] The structure of arbuscular mycorrhizaehas been highly conserved since their first appearance in the fossil record,[8] with both thedevelopment of ectomycorrhizae, and the loss of mycorrhizae, evolving convergently onmultiple occasions.[9]Types of mycorrhizaArbuscular mycorrhizal wheatPlant anatomy, From Wikipedia, the free encyclopedia 244
  • 245. Ectomycorrhizal beechAn ericoid mycorrhizal fungus isolated from Woollsia pungens.[10]Mycorrhizas are commonly divided into ectomycorrhizas and endomycorrhizas. The twogroups are differentiated by the fact that the hyphae of ectomycorrhizal fungi do notpenetrate individual cells within the root, while the hyphae of endomycorrhizal fungipenetrate the cell wall and invaginate the cell membrane.EndomycorrhizaEndomycorrhiza are variable and have been further classified as arbuscular, ericoid,arbutoid, monotropoid, and orchid mycorrhizae [11]. Arbuscular mycorrhizas, or AM(formerly known as vesicular-arbuscular mycorrhizas, or VAM), are mycorrhizas whosehyphae enter into the plant cells, producing structures that are either balloon-like(vesicles) or dichotomously-branching invaginations (arbuscules). The fungal hyphae donot in fact penetrate the protoplast (i.e. the interior of the cell), but invaginate the cellmembrane. The structure of the arbuscules greatly increases the contact surface areabetween the hypha and the cell cytoplasm to facilitate the transfer of nutrients betweenthem.Arbuscular mycorrhizae are formed only by fungi in the division Glomeromycota. Fossilevidence[8] and DNA sequence analysis[12] suggest that this mutualism appeared 400-460million years ago, when the first plants were colonizing land. Arbuscular mycorrhizas arefound in 85% of all plant families, and occur in many crop species.[9] The hyphae ofarbuscular mycorrhizal fungi produce the glycoprotein glomalin, which may be one ofthe major stores of carbon in the soil. Arbuscular mycorrhizal fungi have (possibly) beenasexual for many millions of years and, unusually, individuals can contain manygenetically different nuclei (a phenomenon call