TAXUS............................,....pptx

Taxus

1. TAXUS

2. CLASS : CONIFEROPSIDA ORDER : CONIFERALES FAMILY – TAXACEAE

3. TAXUS BACCATA

4. MORPHOLOGY Small medium sized tree – evergreen – 9 to 20 m tall. Stem – short – upto 7 m girth – red-brown bark – peels off easily. Branches spreading – surrounded by scales at base – shoots bear leaves. Leaf – close spiral arrangement – but spread due to twisting & curving of petioles. Lamina – asymmetrical at base – narrow at the petiole – entire, dark green, glossy with recurved margins & pointed spiny tips – a single median vein very prominent. Root – typical tap root.

5. ANATOMY Root – Epidermis with unicellular hairs when root young. Cortex – parenchymatous – large cells with intercellular spaces. Endodermis – single layered. Pericycle – multilayered . No resin canals in cortex – but resin parenchyma present. Root is diarch – with uniserate pits. Sec.growth as in Pinus.

6. Stem : Young stem with long ridge-like leaf cushions. In old stems – these scale off. Epidermis – parenchymatous – cuticularized – some cells contain tannin. Cortex parenchymatous – resin canal & resin parenchyma absent in cortex & wood. Endodermis – single layered. Pericycle – single layered. Vas.bundles – same as in other coniferales . Xylem with uniseriate bordered pits. Pith parenchymatous. Sec. growth starts at early stage – distinct annual rings present. Tracheids arranged in radial rows – with bordered pits & uniseriate rays.

7. Leaf – dorsiventral – upper & lower epidermis – rectangular parenchymatous. Upper epidermis with thick cuticle & lower epidermis with thin cuticle. Stomata – haplochelic - on lower epidermis only. Mesophyll comprised of palisade & spongy. Palisade 1 to 2 layers below upper epidermis. Spongy – loosely arranged & chlorophyllous . Sclerids present here & there. Vas.bundle – single with prominent bundle sheath – sclerenchymatous . Transfusion tissue very conspicuous on either side of bundles. No resin canals.

8. REPRODUCTION Heterosporous – dioecious. Male & female trees morphologically alike till bearing reproductive structures. Male cone – singly seen – globose heads – stalked & axillary. Cone axis with few deccusate , sessile, decurrent- imbricate scales & 6 to 14 radially symmetrical spirally arranged, perisporangiate microsporophylls – peltate as in Equisetum. Each sporophyll bears 6 to 8 microsporangia – pendant & elongate – do not hang freely but are fused with stalk on the inner side.

9. Female cone – not organised into a typical cone – an axillary shoot bud develops on a branch – protected by many scales – apical meristem of the shoot transforms into ovule – nucellus & integument are formed – ovule is terminal & cauline in origin – scales are sterile megasporophylls – cone axis itself produces a fertile ovule – unitegmic, crassinucellate , sessile & orthotropus .

10. Integument free from nucellus except at base. When young ovule - ring-like out growth - the aril develops from base of integument – covers the entire ovule. Aril – green saucer-shaped – in the beginning & large flesh red cup later with a hard bony seed.

11. POLLINATION Wind dispersal – pollen uninucleate at time of dehiscence – ovule is inverted at the time of pollination – hanging drop at ovular tip – pollen germinates at nucellar beak – pollen tube single – carry the functional male gamete.

12. FERTILIZATION Pollen 4 –nucleate when it reaches the egg. Tube, stalk & non-functional male gamete – absorbed at the upper end of the egg. Functional nucleus moves to center to fuse with egg nucleus.

13. SEED Thick fleshy aril around seed. Aril epidermis with several stomata. Seed coat – three layers Additional aril also present.