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PINUS- Arya Baiju.pptx msc botany plant structre

Pinus is a key genus in the Coniferales order, with around 105 species primarily found in the northern hemisphere, including six native species in India. The tree exhibits distinct morphological features such as a well-developed tap root, monopodial branching, and two types of leaves: scale and foliage leaves. Its reproductive process involves anemophilous pollination resulting in the formation of male and female cones, with seeds germinating after a year, leading to the growth of the primary root and axial shoots.

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PINUS Division: Gymnospermae CIass: Coniferopsida Order: Coniferales Family: Pinaceae Genus: Pinus ARYA BAIJU MSc BOTANY – 1ST SEM
DISTRIBUTION • Pinus is the most important genus of coniferales. • About 105 species distributed throughout the northern hemisphere. • It forms dense evergreen forests in the hill tracts of northern temperate and sub- alpine region. • In India there are six indigenous species ,namely P.roxburghii, P.Wallichiana, P.Gerardiana, P.Merkusii, P.Insularis and P.Armandi. • Several Exotic species have been introduced to India(P.laricio, P.montana and P.sylvestris)
EXTERNAL MORPHOLOGY • Pinus is an evergreen perennial tree growing in temperate xerophytic habitats. • Young plant is pyramidal in appearance with its horizontal branches arranged in regular whorls. • In mature tree crown become rounded ,flat or spreading. • The plant body is differentiated into root, stem and leaves. Roots : Pinus has well developed tap root. It remains short and grows on hard ground or rocks. the lateral roots are well developed. These roots spread over a large area. Young roots are infested with fungus to form mycorrhizae.
STEM: the main stem is cylindrical, erect ,branched and woody .The Branches are monopodial and develop spirally in the axils of scale leaves. The spiral banding gives the plant a conical or pyramidal appearance. Branches of pinus are dimorphic . There are two types of branches a. Long shoots of unlimited growth - The main branches have an unlimited growth. They bear only scale leaves. b. Dwarf shoots of limited growth - Branches of limited growth or dwarf branches are produced in axil of the scale leaves on the main branches. These are about 1-2cm long . These are covered by one or two scale leaves. These branches also bear foliage leaves. A dwarf shoot with foliage leaves is called spur.
Leaf: pinus has two types of leaves : scale leaves and foliage leaves. a. Scale leaves - The scale leaves are small ,membranous and brownish in colour. These are protective in function. They are present on the main and dwarf shoots. b. Foliage leaves- the foliage leaves are green and needle like. They are found only on the dwarf shoots forming the spur.
ANATOMY • INTERNAL STRUCTURE OF LEAF 1. Epidermis Leaf is covered by thick walled epidermis. Epidermis is covered by a thick layer of cuticle. Sunken stomata are present below the general surface. Two or three layered hypodermis is present underneath the epidermis. Hypodermis is composed of sclerenchymatous tissues. Hypodermisd is the main strengthening tissue of the leaf. 2. Mesophyll The mesophyll of the leaf is parenchymatous.it is not differentiated into palisade and spongy parenchyma. Resin canals are present below the hypodermis. Each resin canal is lined by a layer of small epithelial cells. Each leaf is supplied by two unbranched veins.
3. Endodermis And Vascular tissues - Endodermis is present outside the pericycle. Pericycle surrounds the xylem. Pericycle is formed of parenchymatous cells. Its cells adjacent to the phloem are called aluminous cells. The cells adjacent to the xylem are called tracheid cells. These specialized cells form the transfusion tissue. They help in the lateral flow of nutrients. • Internal structure of root Young root is di-to pentarch .xylem bundles are y shaped. The ring of vascular bundles is surrounded by two or three layered pericycles . Pericycle is surrounded by endodermis. The cortex consists of a few layers of thin walled parenchymatous cells. Root hairs may be present or absent. Roots may be covered by mycorrhizal fungus.
• Internal structure of stem Stem is differentiated internally into epidermis, cortex, vascular tissue and central pith 1. Epidermis The surface is covered by an epidermis. It consists of a single layer of cells. Outer walls of these cells are highly cutinized. Below the epidermis is a hypodermis which is formed of layers of lignified cells. 2. Cortex The cortex is formed of parenchymatous cells. Cortex has a large number of resin canals. Each resin canal is surrounded by a layer of resin secreting glandular epithelial cells.
3. Vascular bundle The vascular bundle are conjoint and collateral. They form a ring around the pith. In each vascular bundle the xylem is towards the inner side and phloem towards the outer side. a narrow strip of cambium is present between xylem and phloem. Pericycle is present outer to the ring of vascular bundles . A single layered thin walled endodermis is present outside the pericycle . Secondary growth takes place by the activity of cambium ring . Distinct annual rings in the wood 4) Bark Phellogen originates in the deeper layers of the cortex. It is present in the form of strips. It produces characteristic scaly bark.
REPRODUCTION MALE CONE • Staminate strobili • Microsporangia bearing cones • Form in clusters on axils of the scale leaves of long shoots small oval structure. • It has central axis which bears spirally arranged microsporophylls. • Microsporangia sessile, sac-like, seen on lower surface of microsporophyll development of microsporangia is eusporangiate . • Mature microsporangium has thick, multilayered wall. • Tapetum: innermost nutritive layer, disintegrates at maturity • Sporangial wall encloses sporogenous tissue ;consist of microspore mother cell. • Microspore mother cell by meiotic division form 4 haploid spores.
• At maturity, a single microsporangium contains numerous pale yellow pollen grains. • Pollen grain has 2 layers ,outer exine and inner intine. • Exine on lateral sides has 2wings. • Anemophilous pollination • Pale yellow pollen grains are released into air,so the forest appears yellow during wind. • Sulphur showers- occurs when pine tree are shaken by strong wind. FEMALE CONE • Singly Or grouply 2-4 • Develop from axils of scale leaves of long shoot. • Take 3years for maturation. • Large ovoid in shape and cylindrical at maturity. • Consists of central axis which bears megasporophylls in acropetal succession.
• Few megasporophyll present at the base and apex are sterile. • Fertile megasporophyll has 2 parts : bract scale and ovuliferous scale • Bract scale-small, thin, arranged spirally on central axis. • Ovuliferous scale-large, thick, woody, present on the upper surface of bract scale with pointed tip apophysis. Each ovule is orthotropous. • Micropyle faces towards the central axis. • Central part of ovule contain nucellus - nutritive layer. • simple integument- 3 layer; outer fleshy, middle stony and inner fleshy pollen chamber is opposite to micropyle. • Nucellus is differentiate into megaspore mother cell. • Megaspore mother cell undergo meiosis to produce 4 megaspores.
• Female cone first year ;oval shape ,compact, pale green, short stalk, megasporophyll close to each other • Second year; large ,red colour, woody,megasporophyll less compact, seed are present inside. • Third year; elongated, woody, megasporophyll loosely arranged, seeds are dispersed. Pollination • Anemophilous pollination during pollination, ovuliferous scales open providing access for pollengrains to ovule • pollen sac open by longitudinal slit releasing pollen grains. • Nucellus break releasing pollination drop from micropyle. • Pollination drop contain sucrose, glucoseand fructose.
• Pollen grains are caught in pollination drop and collected in pollen chamber. • Embryonal Cells : cells of the lower tier become embryonal cells .The embryonal cells separate to form Fertilization • Takes place after 1 year. • Generative cell dividers into tube cell, stalk cell and spermatogenous cell. • Pollengrains germinate and form pollen tube • Spermatogenous cell divides into 2 male gametes which show amoeboid movement . • Pollen tube wall is disintegrated by enzymes secreted from egg and male nuclei is released. • One male gamete fuses with egg and form zygote.
Germination of seed • The Radicle Grows out it splits the testa at the micropylar end • This radicle Grows down in the soil and forms the primary root. • The hypocotyl elongates to form a loop. Then it becomes straight. • It carries with plumule and the cotyledons. • The testa is also carried up with the cotyledons.
LIFE CYCLE
STRUCTURE OF OVULE • Structure of ovule • In pinus two anatropous ovules are formed on the upper side of the ovuliferous scale. • Each ovule consist of a central mass of tissue called nucellus . • It is surrounded by a covering called integument. • Integument arise from the base of the ovule. • Integument is differentiated into a outer fleshy layer, middle stony layer and inner fleshy layer. • The micropyle leads to the top of the nucellus. • Nucellus develops a cup chamber called pollen chamber is present.
• Pollen grains are lodged after pollination in pollen chamber. • In nucellus, towards the micropylar end a single large cells get differentiated called archesporial cell. • It divides periclinally into an outer parietal cell and inner sporogenous cell. • Parietal cells divides and develops into a nourishing layer. • Megaspore mother cell undergoes meiosis and forms a liner tetrad of megaspore of which the basal one is the functional megaspore called the embryo sac cell
REFERENCE • Bryology/Ptreidology/Gymnosperms/Palaeobotany by K.K.Bhaskaran & A.R.Ajith Kumar Ramesh. • Pinus (pine) description - The Gymnosperm Database (conifers.org ) • Pinus : External Morphology and Different Parts (biologydiscussion.com) • Pinus - Description, Life Cycle and Examples (byjus.com)
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