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Botany session 2
1.
© Copyright PCNM
2011 Botany and Pharmacognosy Session 2
2.
© Copyright PCNM
2011 Review Last week we covered: An Introduction to Botany & Pharamcognosy
3.
© Copyright PCNM
2011 This Session During this session we will cover: Angiosperm morphology Stems Roots
4.
© Copyright PCNM
2011 Angiosperm morphology • Morphology is the outer form of the flowering plant. It covers the external structure of plant parts, such as leaves, roots, stems, buds, flowers, fruits and seeds
5.
© Copyright PCNM
2011 Monocotyledons and Dicotyledons. • Cotyledons are parts of the embryo within the seed of a plant. Upon germination they become the embryonic first leaves of a seedling. The number of cotyledons possessed by an angiosperm is one characteristic used to classify them. Species with one cotyledon are called monocotyledons, and those with two are termed dicotyledons. • Cotyledons are quite different in appearance to the true leaves of the seedling which only develop after the seed has germinated.
6.
© Copyright PCNM
2011 Monocots and dicots have other distinguishing features. • Feature Monocotyledon Dicotyledon • Leaf structure Parallel veins Network veins • Roots Fibrous roots Tap roots • Stem Soft Hard • No. of cotyledons 1 2 • Number of petals Divisible by 3 Divisible by 4 or 5 • Type of plant Mostly grasses Herbaceous or and similar Woody; herbs, Shrubs or tree
7.
© Copyright PCNM
2011 Basic Plant Organisation • Angiosperms are, like all other living things, made up of cells. • A number of cells of the same type grouped together and concerned with the same function form a tissue. • Two or more tissues closely associated and performing a major function form an organ. • Organs may be grouped into organ systems. • The organs that make up flowering plants are roots, leaves, buds, flowers, fruit and seeds. • Each organ of a plant has one or more functions to perform so that the plant as a whole can survive and produce its own kind.
8.
© Copyright PCNM
2011 The principal functions • Roots • provide anchorage • absorb oxygen, water and minerals from the soil • store food which has been manufactured by other parts of the plant • conduct absorbed materials and stored food to the stem • are sometimes involved in asexual reproductive processes
9.
© Copyright PCNM
2011 The principal functions • Stems • support the leaves and flowers • transport water and minerals from the roots to the leaves • transport food manufactured in the leaves to other parts of the plant • store food and water • take part in asexual reproduction • photosynthesise food if the stems are green
10.
© Copyright PCNM
2011 The principal functions • Leaves • manufacture sugars by photosynthesis • assist in maintaining the water balance of the plant • leaves of some plants take part in asexual reproduction, food storage, climbing and insect trapping
11.
© Copyright PCNM
2011 The principal functions • Flowers • contain the structures for sexual reproduction for the production of fruit and seeds • attract pollinators • Fruit • protects seeds • provides various means of dispersing the seeds to locations favourable for their growth
12.
© Copyright PCNM
2011 The Angiosperm Life Cycle • A typical angiosperm undergoes these events in the life cycle. • 1. Under suitable conditions a seed germinates to produce a seedling • 2. The seedling grows into a mature plant • 3. Flowers form on the plant • 4. Pollen grains form in the anthers, egg nucleus forms in the ovules of the flower • 5. Pollen grains are transferred from the anther to the stigma in the process called pollination. The pollen grain produces a pollen tube which grows down the style to enter an ovule in the ovary The pollen tube discharges sperm nuclei into the ovule. A sperm nucleus unites with an egg nucleus to form a zygote in the process called fertilisation.
13.
© Copyright PCNM
2011 The Angiosperm Life Cycle • 6. after fertilisation the flower withers, except for the ovary. A fruit and seeds form. Note that in angiosperms the seeds are fully protected enclosed within the fruit. • This process is sexual reproduction. • The sexual reproduction of any organism, whether animal or plant, is defined as the union of two gametes or gametic nuclei resulting in the formation of a zygote. The zygote is the beginning of the formation of a new individual
14.
© Copyright PCNM
2011 The Angiosperm Life Cycle • A gamete is a reproductive cell. It has only one set of chromosomes. It is said to be haploid. In plants the male gametic nuclei are the sperm nuclei produced in the germinating pollen grain. The female gametic nucleus is the egg nucleus produced in the ovule. The zygote is formed from the fusion of the sperm nucleus and the egg nucleus. Thus the zygote has two sets of chromosomes. It is said to be diploid. • The most important feature of sexual reproduction is that the offspring are usually different from one another and from their parents. This is termed variability. • In plant and animal breeding when the parents are genetically similar the offspring are also genetically similar. These individuals form a pure line.
15.
© Copyright PCNM
2011 The Angiosperm Life Cycle • Asexual reproduction results in offspring which are identical to the parent and to one another. • Asexual reproduction is any form of reproduction that does not involve the fusion of haploid gametes or gametic nuclei. New plants are produced from parts of the parent plant which already have two sets of chromosomes. Such parts include stems, leaves and roots. No pollination or fertilisation processes are involved. • In botany, asexual reproduction is often referred to as vegetative reproduction.. It is very important in the lives of many flowering plants.
16.
© Copyright PCNM
2011 The Angiosperm Life Cycle • Vegetative reproduction can occur naturally or artificially through manipulation by humans.
17.
© Copyright PCNM
2011 Natural • Many angiosperms have modified structures which can store food which can help a plant survive unfavourable periods and then provide for rapid growth when growing conditions are once again favourable. These structures are modified stems or roots. New plants can also arise from these structures. For example, the tuber of a potato is an underground stem and the tuber of a sweet potato is a swollen root. These possess ëeyesí from which new individuals can grow. • Plants such as onions and daffodils produce bulbs. Bulbs are thickened, fleshy usually subterranean buds, growing roots from the underside and stems, flowers and foliage from the crown. Bulbs can split into two bulblets which will grow to produce identical daughter plants. Some bulbs produce tiny bulbils from their base. These will all grow into plants identical to the parent plant. Note that bulbous plants can also reproduce sexually to produce seeds.
18.
© Copyright PCNM
2011 Natural • Other bulb-like structures which reproduce asexually are corms., such as found in the gladiolus and the crocus. Corms are underground sections of stem, consisting of fleshy tissue with a bud at the top. Tiny cormels are produced at the base of the corm. These will eventually grow to a mature plant identical to the parent. • Rhizomes are underground stems. They possess nodes from which roots and shoots can grow, forming a new individual. The ginger plant has rhizomes. • Stolons are above ground stems which grow out from the parent plant and produce roots and leaves to form a new plant. Strawberries reproduce asexually using stolons. • Some plants can reproduce asexually by producing new plants from the parent leaves. Begonias are an example of this.
19.
© Copyright PCNM
2011 Artificial • Using various techniques man can increase the numbers of a plant by asexual means. Stem cuttings, root cuttings and even leaf cuttings all produce plants identical to the parent. Adventitious roots grow from the end of the cutting and a new plant is formed. • Micro-propagation is used commercially to produce large numbers of plants from a small piece of tissue. Vegetative buds of a plant such as an orchid are divided into individual cells. These are cultured under special conditions in a laboratory. The cells divide and produce new plants, each identical to the parent plant. Each culture can produce many new plants, often thousands at a time, which are identical to the parent plant. Note that this is NOT genetic engineering. • The benefits of artificial or tissue culture reproduction is that large numbers of plants with special characteristics can be produced in a short period of time.
20.
© Copyright PCNM
2011 Checkpoint!
21.
© Copyright PCNM
2011 Roots • The root systems of many plants seem to be disproportionately extensive. However, root systems need to be large enough to meet the requirements of all the aerial parts of the plant so that it can survive and reproduce. • The major functions of the roots are: • Anchorage and support. Plants need to be firmly anchored in the soil so that the above ground parts of the plant are supported and the plant does not blow over in normal strength wind • Absorption. The roots need to be able to absorb from the soil oxygen, water and minerals in solution. • Translocation. The roots need to be able to conduct absorbed materials to the stem to reach the rest of the plant. • Storage. Roots can store water, nutrients and carbohydrates, especially at times when the plant is dormant.
22.
© Copyright PCNM
2011 Kinds of Roots • Taproot system. • When a seed from a dicotyledon germinates a single root grows vertically down into the soil. Lateral roots arise from this primary root, and smaller roots arise from these lateral roots but the primary root remains the largest and dominant root, the taproot. Taproots are capable of growing deep down into the soil some taproots are modified to store food, as seen in the carrot and other root vegetables.
23.
© Copyright PCNM
2011 Kinds of Roots • When a monocotyledon seed germinates a single root first appears. This is then followed by lateral roots called seminal roots. This juvenile root system is soon replaced by a number of roots growing from the base of the stem of the plant. These are adventitious roots. Smaller roots then develop from these adventitious roots. The end result is a tuft of shallow roots of similar size arising from the base of the stem. This fibrous root system, shallower than the tap root system, is found in monocots such as grasses, lilies and palm trees.
24.
© Copyright PCNM
2011 Kinds of Roots • Adventitious roots. • An adventitious root is one which grows from some part of the plant other than a pre-existing root. • Adventitious roots form the main roots of the fibrous root system because they arise directly from the base of the stem. • Adventitious roots can grow out from the stems of climbing plants, giving extra support to the plant. These roots are also able to absorb water and mineral salts, and can replace a root system should it be destroyed Climbing ivy develops these roots. Corn and maize plants grow prop roots from the stem just above ground level. These grow down into the soil to provide additional support. Some plants produce adventitious roots from leaves. New plants of African violets can be propagated in this way.
25.
© Copyright PCNM
2011 Kinds of Roots • Many plants can be grown from cuttings. This involves the development of adventitious roots. The new plants are complete plants but have an adventitious root system, even if they are dicotyledons. A dicot grown from a cutting will develop several large lateral roots but not a dominant taproot. Note that this adventitious root system is not the same as the fibrous root system of a monocotyledon.
26.
© Copyright PCNM
2011 General Root Structure • Mature roots are generally coloured brown. Young roots are white and do not contain chlorophyll, with the rare exception of the aerial roots of some orchids. • Roots do not bear leaves although they may have adventitious buds Note that when we come to discuss stems we will see that an underground stem has scale leaves and axillary buds.
27.
© Copyright PCNM
2011 General Root Structure • Young roots form at the extremities of older roots. • The root cap is located at the root tip. Its function is to protect the delicate apical meristem from damage as the root grows through the soil. The outer part of the cap is continually worn away by the abrasive action of soil particles. The apical meristem produces new cells to replace these old ones. • The apical meristem is made up of cells capable of dividing to produce new cells. Some of these new cells replace old root caps cells, others remain in the meristem and still others add to the region of elongation.
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2011 General Root Structure • The region of elongation lies behind the meristem. As the cells in this region mature to full size they push the apical meristem and root cap down into the soil. • Roots become longer as a result of cell division in the apical meristem and the enlargement/elongation of cells in the region of growth.
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2011 General Root Structure • Root hairs are tiny, finger-like outgrowths from the cells of the outer covering of the root, the epidermis. They are located just behind the region of elongation. They are not found in the root tip or in older parts of the roots. The region where the root hairs grow looks fuzzy • The function of root hairs is three-fold: • They grow out from the root in between soil particles. Their cell walls adhere to soil particles, which helps to keep the plant firmly rooted in the soil. • Thee second function is absorption of water, oxygen and nutrients in solution. The root hairs greatly increase the surface area of the root tip because there are millions of root hairs in a root system • Their third function is to reduce soil erosion from wind or rain because the cell walls adhere to soil particles which do not easily wash off.
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2011 General Root Structure • Roots exhibit positive geotropism. This means they grow down towards the centre of the earth. Shoots exhibit opposite behavior, growing up away from the earth. It is believed that roots and shoots act like this under the influence of plant growth- regulating hormones called auxins.
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2011 Soil • Soil is the natural environment for most roots. • Soil is composed of: • Particles of sand, silt and clay • Soil dwelling organisms • Organic substances from partially or completely decomposed plant and animal material • Air • Water with nutrients in solution.
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2011 Soil • Sand and silt are formed by the weathering (physical break-up) of rock. • Sand particles range in size from 2mm to 0.02 mm diameter. • Silt particles are smaller than sand particles. • Clay is composed predominantly of minerals formed as products of secondary, chemical weathering. The rock minerals undergo a chemical change before becoming clay minerals. Clay particles are very small, 0.00005mm and smaller. Clay usually contains aluminium silicate.
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2011 Soil • In between the particulate matter making up soil are pore spaces. There are larger macropores which hold air and smallmicropores containing water. Air provides the oxygen required by roots for respiration to produce energy for growth, and the water held in the micropores is the most important source of water for plants. • Soil with a combination of macro and micropores provides the best medium for root growth. Roots cannot grow in water-logged soil as there is insufficient air in the macropores. Equally, water cannot grow in soil without water. Roots generally grow towards moisture, as is evidenced by roots clogging up drainpipes!
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2011 Modified Roots • The roots of some plants have functions beyond those of anchorage and absorption. Many plants have roots modified for food storage. When a root is modified for food storage it is known as a tuber. Tubers are found in biennial and perennial plants. Plants with taproots modified as tubers include root vegetables such as carrots, turnips, radish and beetroot. Plants with tuberous adventitious roots include the sweet potato, the dahlia and the day lily. • Some plants produce aerial roots which grow from above ground stems. Some climbing plants use aerial roots for attachment or support. Climbing ivy is an example. Other plants produce aerial roots which can absorb moisture from rain. Some orchids have thickened, whitish aerial roots which absorb and store moisture. Crucifix and vanda orchids produce aerial roots with green tips which can carry out photosynthesis.
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2011 Modified Roots • Prop roots are adventitious roots which arise from nodes above the ground. They then grow down into the soil where they branch extensively and provide additional support. These roots can also absorb water, nutrients and oxygen. Some mangrove trees produce prop roots as do pandanus, some palms and maize. • Mangrove trees growing where they are regularly underwater develop respiratory roots. These grow from underground roots but grow vertically up out of the water. These roots are called pneumatophores and they absorb oxygen for the plant.
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2011 Modified Roots • Plants from the Fabaceae family develop nodules on their roots. These nodules are formed by Rhizobium bacteria which are able to fix nitrogen so that it can be absorbed by plants. Nitrogen is essential for plant growth as it makes plants green, thus enabling photosynthesis to take place. Plants cannot absorb gaseous nitrogen but can absorb the mineral form of nitrogen converted by these bacteria. Many Australian plants are able to fix nitrogen, an essential function as Australian soils are of very poor quality. • Banksia, Grevillea and Hakea are members of the Proteaceae family They develop dense clusters of tiny lateral feeder roots. These proteoid roots increase the surface area of root hairs so that more nutrients can be absorbed from the very infertile soils found in much of Australia.
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2011 Modified Roots • Some plants are parasitic, that is they obtain nutrients and water, and sometimes food, from another, host, plant. The roots of parasitic plants develop suckers called haustoria which attach to the roots of host plants from which they absorb water or nutrients. The do not take up substances directly from the soil. The WA Christmas tree, Nuytsia floribunda, is a parasite. • Some plants are stem parasites. Their roots do not enter the soil but attach to the stem of the host plant. The haustoria penetrate the bark of the host stem and absorb nutrients and water. In many instances the parasite kills part or all of the host plan
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2011 Checkpoint!
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2011 Stems • Functions: • To conduct water and dissolved mineral salts from the roots to the leaves • To carry manufactured sugars from the leaves to other parts of the plants in the process of translocation. • To hold leaves in a suitable position for maximum photosynthesis • To hold the flowers up to allow easier pollination • Stem structure. • Young stems are usually herbaceous, that is green and soft. • As a perennial stem matures it becomes thicker and harder, and develops bark. Woody tissues develop inside. These increase the girth of the trunk and support the canopy. Stems can become very large in this way especially in trees.
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2011 Stems • Young stems usually have a smooth surface or are covered in hairs. • Lenticels are small pores which develop on some stems to allow oxygen to penetrate into deeper tissues. Lenticels are seen mainly on cool temperate trees and shrubs which need to survive cold wet soils during winter. Australian native plants do not usually have lenticels, so they are very susceptible to death from waterlogging. Many mangroves contain lenticels and can survive periodic inundation. • Stems bear leaves and buds. The place where leaves attach to the stem is called a node. The area between two nodes is the internode. • Organs which may be attached to stems are leaves, buds, flowers and fruit.
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2011 Buds • A bud is an undeveloped, immature shoot or flower. • Vegetative buds develop into leafy shoots. Floral buds develop into single flowers or inflorescences. An inflorescence is a group of flowers. • A mixed bud grows to become a leafy flowering branch or shoot. The Australian bottlebrushes, Callistemon species, bear mixed buds. • Buds are also named according to the position they occupy on the plant. A terminal bud is located at the apex (top) of a stem. An axillary or lateral bud is located in the axil of the leaf. The axil is the angle between a leaf and a stem. • If a stem ends in a vegetative bud it can continue to grow, and is said to have indeterminate growth. When a stem ends in a floral bud, further growth ceases. This stem shows determinate growth. Some stems may end in a mixed bud, such as is seen in Callistemon.
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2011 Adventitious Buds • An adventitious bud is one which arises on any part of a plant other than the normal terminal or axillary positions. A few plants develop buds on roots, as in sweet potatoes, or on the edge of leaves. Kalanchoes develop buds on their leaves, hence one of their common names, Mother of thousands, as adventitious buds on roots or leaves can grow into new plants when conditions are favourable. • The spider plant, Chlorophytum cosmosum, has adventitious buds in the inflorescence stalks which develop into tiny plants. • These adventitious buds are examples of vegetative propagation.
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2011 Epicormic growth • Adventitious buds are also found in the trunks and branches of many shrubs and trees endemic to fire prone regions. Endemic means native to a particular region. After fire, these buds develop epicormic growth, which is the development of new shoots along the trunk and mature branches where new shoots would not normally develop. Some trees and shrubs develop lignotubers, and after fire the buds on the lignotuber can re-shoot. A lignotuber is a starchy swelling of the root crown found in some plants from fire prone areas .Lignotubers will be examined in more detail later in this session. The lignotuber contains buds from which new shoots can develop. • Note: if a tree is not correctly pruned but simply lopped, it can develop epicormic growth from below the cuts. The branches that develop are weak and subject to wind damage, so can be dangerous.
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2011 Modified Roots • Vegetative buds consist of many tiny, immature leaves wrapped around an apex of young dividing cells called the apical meristem. The outermost leaves are often thicker and tougher, and may be coloured brown or black. These are the bud scales and they protect the bud from disease, extremes of temperature and damage from birds and insects. A Brussels sprout is a large vegetative bud and a cabbage head is a giant vegetative terminal bud. • Most vegetative buds grow into new shoots. A terminal bud grows to extend the height of a plant and an axillary bud grows into a leafy branch. Some vegetative buds grow to form tendrils and leaves.
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2011 Modified stems • Stems can be modified for several purposes: • Vegetative reproduction • Storage of water, nutrients and food • Protection of dormant buds in adverse seasons • Protection against grazing animals • Climbing
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2011 Stems for vegetative reproduction • Stolons and runners are slender stems that grow horizontally just above the ground. A stolon has longer internodes than a runner, and only alternate nodes develop. The terminal bud touches the soil, develops adventitious roots and then grows into a new, independent plant. Strawberry plants reproduce vegetatively by stolons. • Runners develop adventitious roots at every nodule. Lawn grasses such as kikuyu and buffalo spread by runners.
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2011 Stems for vegetative reproduction • Rhizomes are horizontal underground stems. They store food which has been translocated from the above-ground leafy shoots. Along the rhizome are brown reduced leaves called scale leaves. These scale leaves have axillary buds which develop into lateral shoots in the leaf axils. There is a terminal bud which develops into a leafy shoot. Adventitious roots develop at the nodes. Ginger, bamboo and mint have rhizomes, as do the Western Australian native kangaroo paw and blue lechenaultia.
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2011 Stems for vegetative reproduction • Suckers are underground shoots which develop into new plants. A sucker comes from a root. Roots do not normally develop buds but some species have the ability to do so if the roots have been damaged in some way. When stimulated by damage to the root, the meristem tissue in the root divides to produce a shoot. Plants which produce suckers include poplars, the powton tree, wisteria, members of the rose family, including some old varieties of fruit tree rootstock, and the herb Taraxacum -dandelion.
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2011 Stems for vegetative reproduction • Stem tubers are the swollen ends of underground stems. The ends of the roots of the potato plant swell to form a swollen tuber. The eyes of the potato stem tuber are made up of scale leaves and axillary buds. Each eye can produce a new shoot in the following year, using the food stored in the tuber. Jerusalem artichokes, the Gloriosa lily from Africa, and the donkey orchid from Western Australia all produce stem tubers.
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2011 Stems for vegetative reproduction • A corm is formed by the enlargement of an underground stem base. In a young corm, leaf bases form protective scales around the corm. In an older corm only leaf base scars are seen forming circles around the corm. Axillary buds are found in the axils of these leaf bases, and a terminal bud is present at the upper end of the corm. In spring the food stored in the corm enables the terminal bud to grow quickly into a flowering shoot above the ground. Later in the season the leaves send food down below ground but it is not stored in the old corm. Instead it goes to the base of the stem immediately above the old corm; this stem base then swells and forms a new corm on top of the old shrivelled corm. The problem of new corms developing on top of the old corm and therefore being too close to the soil surface is solved by the new corm producing contractile roots. Parts of these roots contract and pull the corm deeper underground. Gladioli, the autumn crocus and the saffron crocus all produce corms.
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2011 Stems for vegetative reproduction • A bulb is a condensed shoot. The stem of the shoot is very short and never grows above the soil. Food is stored in the fleshy leaf bases, which are very close together and wrap around one another. The outermost leaf bases are dry and scaly. There is a terminal bud which grows rapidly into a flowering shoot when conditions are favourable. Axillary buds in the axils of the leaf bases may grow into new plants. During the growth season some of the food made in the leaves above ground is sent underground to the leaf bases. This provides energy for growth in the axillary bud to form a new bulb, another form of vegetative reproduction. Onions, garlic and other members of the Allium family produce bulbs. Oxalis is the only dicotyledon plant to produce true bulbs.
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2011 Cladodes and Phylloclades • In some plants the stems are modified to resemble leaves. They are green when young so can photosynthesise like true leaves. True leaves may be absent except on very young stems, or they may be modified into scales or spines. Flowers may grow from the edges or even out of the flat surface of the stem. • A cladode is a stem with limited terminal growth, often for only one or two internodes. Short cladodes may branch out from the node on the main stem. Asparagus produces short cladodes, as does the Australian native she-oak, Allocasuarina. • A phyllocladode is a stem which can keep on growing, showing regular nodes and internodes. Buds develop in the nodes and along the stems, and may result in flowers or lateral branches. The zygocactus, Schlumbergera, bears phyllocladodes. The true leaves are modified into fine spines which surround the base of the floral buds
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2011 Cladodes and Phylloclades • Some plants store water in an enlarged swollen stem. This enables them to survive drought or the tropical dry season. The boab tree from the north west of Western Australia, Adansonia gregorii, and the ponytail palm, Beaucarnea recurvata, from Mexico, store water in this way. • A lignotuber is a large underground modified stem. Lignotubers are a feature of many Australian native trees and shrubs. They store food and are fire and drought resistant. If the main trunk of the tree is destroyed by fire, wind damage or drought, the dormant adventitious buds in the lignotuber will develop. The resulting re- growth will be as a multi-stemmed tree rather than a single trunk.
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2011 Cladodes and Phylloclades • Spines, thorns and prickles are modified sharp structures found on certain plants. A spine is a modified leaf, such as found on cacti. • Prickles are modified hairs, for example, rose prickles. • A thorn is a modified shoot. It develops from a bud in a leaf axil. In some species this bud develops into a short shoot with its own leaves and with the terminal bud replaced by a strong, sharp thorn. It is suggested that thorns are defence mechanisms developed especially by plants growing in sandy soil which does not provide adequate resources for fast regeneration. Plants with thorns include lemon trees and bougainvillea. • Prickles develop out of the surface cells of a stem. They are found along the internodes, not just at a node as with spines and thorns. As already mentioned, roses bear prickles, not thorns.
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2011 Cladodes and Phylloclades • A tendril is a structure modified for climbing. Tendrils may develop from leaflets, buds, and from the central stalk-the rachis- of an inflorescence. Remember that an inflorescence is a cluster of flowers on a stem. • Tendrils from buds develop in the leaf axil, as seen in passionfruit. Peas have tendrils that develop from modified leaves that emerge from a leaf node. • The tendrils of grape vines are also modified buds. The leaves are arranged alternately along the stem with a bud developing from the same node. Some of these floral buds develop into bunches of grapes while others are modified to develop into tendrils to support the vine. • The internodes of some thin, flexible stems also twine around support to climb. Jasminum polyanthum, pumpkins and cucumbers are twiners.
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2011 Cladodes and Phylloclades • Modified stems can be identified by the following characteristics they possess: • A leaf-like structure such as scale leaves or leaf bases or the scars where they have been • Nodes and internodes • A terminal bud • Axillary buds in the axils of leaf-like structures
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2011 Advantages of food storage in modified stems • Food storage in modified stems such as rhizomes, corms and stem tubers makes it possible for there to be very rapid growth under favourable conditions, such as the warmer, longer days of spring. Plants that can grow early are then able to flower and set seed before there is competition from other plants for water, mineral salts and light. This can be used to manís advantage, for example growing a crop of potatoes from pieces of potatoes containing eyes, rather than growing them slowly from seed. It also means the same strain of potato can always be produced. • Plants with underground food stores are able to be persistent, that is they can survive and grow even if their aerial shoots are destroyed for some reason. This does have the disadvantage of making weeds with underground food stores extremely difficult to eradicate, such as oxalis.
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2011 Non-modified stems for propagation • Modified stems enable vegetative reproduction to occur in nature. Man can replicate plants vegetatively by taking cuttings of stems which would not normally reproduce. • Softwood cuttings are the young, soft tip shoot growth. Lavender, sage and rosemary will propagate readily from soft tip cuttings. • Semi-hardwood cuttings are taken from young growth several months old and just beginning to mature. Shrubby plants such as hibiscus and camellia are propagated in this way. Rosemary can be propagated in this manner. • Hardwood cuttings are taken from mature growth a year old, often from a deciduous plant. Rootstocks of roses and fruit tress are obtained this way. The bay tree is also propagated from hardwood cuttings.
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2011 Checkpoint!
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2011 Summary Today we have covered; Angiosperm morphology Stems Roots
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2011 Next Session We will cover: • Leaves
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2011 Preparation Brief Notes • Don’t forget to log on to the LMS and download and print off your brief notes and handouts for the next session.
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