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PODOCARPUS...........................pptx

The document provides a detailed description of Podocarpus, a genus of tall, evergreen trees from the family Podocarpaceae, highlighting their morphology, anatomy, and reproductive processes. It covers aspects such as leaf structure, root anatomy, and the characteristics of male and female cones, including pollination and seed development. Additionally, it mentions embryogeny and germination, emphasizing the dioecious nature of the plants and the process of cleavage polyembryony.

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PODOCARPUS
CLASS : CONIFEROPSIDA ORDER : CONIFERALES FAMILY : PODOCARPACEAE
MORPHOLOGY • Tall, evergreen trees – innumerable branches – main trunk – 15 m high & 1.8 to 2.5 m girth – young branches green & mature ones brown. • Leaves – linear, flat, sessile, narrow at base & tip – tip pointed in some – scattered on old shoots & crowded on young shoots – leaves twisted at base – so lower side faces up to receive sunlight – with a single midrib – for entire length of leaf. • Root – typical tap root – with mycorrhizal tubercles on main & lateral roots.
ANATOMY • Root – diarch & exarch – parenchymatous cortex with starch & tannin cells – cortical cells get infected with fungus at early stage – parenchyma cells proliferate forming nodular structures or tubercles – tubercle cells infected with fungal hyphae & spores – sec. growth – normal type – but at very early stage.
Stem: Young – has fluted outline due to broad leaf bases – epidermis – thick cuticularised cells. Cortex – narrow parenchymatous. Old stem – outer 3 to 4 layers of cortex & some epidermal cells filled with tannin. Inner cortex with scattered sclerids. Resin canal – outside each vascular bundle. VB – collateral & open. Leaf traces varying from 2 to 3 in cortex. Pith parenchymatous with sclerids & resin cells. Sec. growth early - similar to other gymnosperms. Xylem – with growth rings in wood – tracheids & parenchyma with uniseriate rays. No resin canals in wood. Uniseriate bordered pits present. Cork cambium present.
• Leaf – • Epidermis with thick cuticle. Hypodermis sclerenchymatous on both sides – 1 to 3 layers – followed by palisade – palisade on upper & lower sides. Rest of mesophyll is spongy tissue. • Mesophyll also has fibres & sclerids. Single collateral vascular bundle. • Xylem comprised of tracheids & phloem of sieve tubes & fibres. Transfusion tissue – on either side of vascular bundle – thick walled & running parallel to lamina. • Resin canal number varies in species – P. gracilior – 1 resin canal below phloem. Stomata on either sides – sunken – arranged in parallel rows.
REPRODUCTION • Plants heterosporous – dioecious. • Male cones on short lateral branches – axillary – each branch has 1 to 3 male cones – short stalk – 2cm long & 3 to 4 mm thick. Numerous spirally arranged sporophylls – each terminates into a large triangular, upward projecting tip – two sporangia in each – on either side of stalk - ovoid in shape on lower side – dehisce transversely.
• The female cone in many species is so highly reduced that it is represented only in the form of a swollen fleshy receptacle with a single terminal ovule. In some other species, however, the ovules are borne in cones. • Female cones – axillary – at apex of fertile branch – cone is 2.5 cm long – with 5 to 10 leafy bracts. Uppermost bract – fertile with single ovule in its axil. Ovule – ovoid, unitegmic, anatropus & covered with shiny waxy deposition. Sterile bracts fuse to form a fleshy receptacle on which seed is borne. Receptacle is brightly coloured when old & is edible. Ovuliferous scale surrounds the ovule completely except at micropyle – this is called epimatium.
• Seed is round – 2.5X2cm, with thick fleshy yellow green seed coat. • MICROSPOROGENESIS • Dev. as in other gymnosperms.
POLLINATION • Winged pollen – wind pollination. • Inverted ovule – pollination drop. • Pollen land directly on the pollination drop. • Pollen are taken in. • Pollen tube grows inward & reaches free nuclear region of gametophyte. • Spermatogenous cell nucleus divides when female gametophyte becomes completely cellular. • 2 nuclei formed – both initially of same size – one grows & moves to center & the other smaller one goes outside & is extruded from the cell. • Only one functional male nucleus.
• FERTILIZATION -As usual – zygote. • EMBRYOGENY • Zygote nucleus • 16 free nuclei • Some move to upper part & do not contribute to embryo formation (relict nuclei). • 8 in the remaining region – wall formation • Pri. upper tier & Pri. Embryonal tier
• Upper tier has no wall – open tier • Pri. embryonal tier divides - suspensor tier & embryonal tier • Suspensor tier elongates & pushes embryo deep inside. • Embryonal cells – 4 in number – divide to form – groups of 4 cells each – as embryonal tetrads – followed by lobbing – each lobe is an embryonal tetrad. • Secondary suspensors develop, elongate & function as embryonal tubes. • Each embryonal tetrad & tube behaves as an independant embryo. • So there is cleavage polyembryony. • Seed in final stage with a fully developed embryo. • Embryo in the final stage – only 2 cotyledons, plumule & radical.
• SEED – thick seed coat. • Ovuliferous scale & integument forms the seed coat. • Seed coat has 3 zones • Outer – several parenchymatous layers. • Middle – 2 to 3 layers of tannin cells. • Inner – sclerenchymatous cells surrounding nucellus. • GERMINATION – Epigeal –germination takes place above the ground.