Gleichenia............................pptx

Gleichenia

1. Gleichenia Class - Leptosporangiatae Order- Filicales Family – Gleicheniaceae

2. Gleichenia

3. Gleichenia About- 130 sps In India - G.linearis , G.glauca G.glauca only in Eastern Himalayas G.linearis - wide distribution Usually in exposed regions, all are xerophytes and terrestrial

4. Gleichenia

5. Sporophyte Has long, dichotomously branched, prostrate , subterranean rhizome bearing leaves on the upper surface and adventitious roots on the under side Leaves occur in 3 rows though appear to be in single row Leaves- a few feet to 50 mtrs in length Leaves show repeated forking- pseudodichotomy as the rachis growth is arrested and the pinnae below continue to grow

6. The leaflets lobed, the incisions reach almost the midrib so appear as pinnules Has open venation Roots- branched- arranged irregulary / in 3 rows

7. Anatomy Rhizome-C.S. Epidermis- single layer of thin walled colourless cells In some sclerenchymatous and brown coloured No stomata Cortex – many layered, broad, may be fully sclerenchymatous as in G.linearis or outer sclerenchymatous and inner thin parenchymatous region as in G.dichotoma Stele- protostelic except in G.pectinata where it is amphiphloic siphonostele in the internode and solenostele in node. In G.linearis and G.dichotoma – it is mixed protostele

8. Rhizome-C.S.

9. Rhizome-C.S.- continued Endodermis- single layered- has casparian bands Pericycle – few layered, thin walled , surrounds phloem completely Xylem occupies the centre- circular in outline/lobed- usually mixed protostele Protoxylem- small patches at the periphery

10. Petiole C.S. Epidermis- thin walled- single layer Cortex- broad- sclerenchymatous Endodermis- single layer, parenchymatous, does not invaginate the xylem arch Pericycle - few layered, completely surrounds the stele Stele- curved C shape with ends curved inwards It surrounds a central parenchymatous pith Protoxylem in small patches in the concave side of the arch Phloem surrounds the xylem completely

11. Pinnule – C.S. Has lower and upper epidermis, stomata only in lower epidermis Mesophyll uniform homogenous- has large air spaces and chlorenchymatous Stele- circular in outline Vascular bindles collateral Phloem faces lower epidermis Xylem exarch

12. Reproduction Sori - on the ventral side of the sporophyll , no indusium , seated on the lateral veinlet a little behind the vein endings Number of sporangia in a sorus varies from 4- 15 Arise on a circular receptacle In some sps the centre of sorus is vacant, in some at the centre sporangia may be present

13. Sporangium- structure- pear shaped, sessile/ subsessile Jacket- single layered Oblique annulus may be present Next to jacket- 2 layered tapetum Tapetal cells disorganize at maturity to provide nutrition to the young spores At the centre spore mother cells are present which undergo meiosis to form haploid spore tetrads Number of spore in a sporangium varies from 128- 1024 Sporangium splits by a vertical slit caused by the contraction of annulus

14. Sporangium- development On the ventral side of the sporophyll , an elevated circular receptacular surface appears Sporangia arise simultaneouly from the superficial cells of this region Devpt . Is leptosporangiate Initials divide by all the three side Cell cut off earlier form the stalk The three segments formed last form the primary jacket cells

15. Finally periclinal division in the jacket cells form a central archesporial cell and primary jacket cell Archesporial cell divides by periclinal and anticlinal divisions to form two layered tapetum and innermost primary sporogenous cell which by divisions form 32-256 spore mother cells Jacket cells by anticlinal divisions form complete jacket around the sporangium

16. In the jacket certain cells form the annulus The outer tapetal cells remain small and flattened but the inner tapetal cells enlarge and nuclei divide and they become multinucleate Later this layer disorganise and form a nourishing plasmodial fluid for the developng spores

17. Gametophyte Spore-small- two types- Trilete spores or tetrahedral spores ( G.glauca , G.linearis etc Monolete spores or bilateral spore( G.volubilis , G.bifidus etc.) Spore –outer exine / exosporium - smooth Inner intine - thin No chloroplast, has scanty cytoplasm and single nucleus, food stored as oil drops

18. Spore- germination- exine ruptures and intine comes out as projection It divides transversally into ,lower rhizoidal cell and upper prothallial cell Prothallial cell divides by transverse wall to a form 5/6 celled filament with chloroplast The teminal cell of the filament cut off an apical cell with two sides which by further divisions form a elongate cordate prothallus with distinct midrib

19. Prothallus - dorsiventral , green, cordate with convoluted margins Midrib distinct as a narrow groove on the dorsal side and projects on the ventral side Older prothallus may branch Has a thick cushion behind the apical notch and archegonia appear on this cushion on the ventral side Protandrous

20. Prothallus monoecious Antheridia- vary in size in diff.sps, sessile/ subsessile Spherical/ globular usually Has a single layered thin wall, distinct triangular opercular cell Produces numerous multiflagellate antherozoids Antheridia absorb water, swell and throw off opercular cell and the male gametes ooze out

21. Archegonia- in the cushion region behind the notch on the ventral side of the proathallus Archegonium - has distinct neck and venter Neck- 4 longitudinal rows of neck cell, 7- 9 cells in height

22. Has as single binucleate neck canal cell Venter- single ventral canal cell and egg, it is embedded in the prothallus At maturity neck canal cell and ventral canal cell disorganise and the neck opens and a passage for sperm entry is formed

23. Fertilization- sperm enters through the open passage of the neck , reaches the egg and fuses with it to from the dilpoid oospore is formed which lies in the venter

24. Embryogeny Oospore - first cell of sporophytic generation First division of zygote is vertical- to form an epibasal cell and hypobasal cell Next division is transverse- quadrant stage is formed Epibasal half – forms stem and cotyledon

25. Hypobasal half- forms the foot and root Foot- conspicuous and haustorial Primary root grows into soil and primary cotyledon pushes upwards through the notch Stem apex grows by a single apical cell and finally an independent sporophyte is formed