Thursday, 27 May 2021

Morphologically distinct sporophytic and gametophytic generations

 Morphologically distinct sporophytic and gametophytic generations



Pole forms foot and roots, whereas the apical pole BIves rise to shoot apex. In some species the basal pole forms suspensor. The embryo of pteridophytes may be classified into two forms on the basis of polarity : (i) exoscopiC embryo - where the apical pole is directed outward, towards the neck of the archegonium (e.g., Psilotum, Equisetum, Ophioglossum); and (ii) endoscopic embryo directed towards the base of the archegonium (e.g., Lycopodium, Selaginella, Isoetes). where the apical pole is In exoscopic as well as endoscopic type of embryo development the first division of the zygote is transverse.

 Pteridophytes show a typical heteromorphic alternation of generations. Morphologically distinct sporophytic and gametophytic generations alternate with each other in regular succession. The (antheridia) and female (archegonia) reproductive structures develop on the gametophytic prothallus. 

They between the Bryophyta and Spermatophyta (seed plants). Classification of Pteridophytes: are between the Bryophyta and Spermatophyta (seed plants Marsilea, Azolla, Dryopteris, Salvinia are the men common examples of pteridophytes Called archegonium. It produces an egg. sporophyte called embryo. The embryo grows into ster-1).

The life cycle shows heteromorphic alternation of The male sex organ is called antheridium. It is a The female sex organ is a flask-shaped structure The diploid zygote gives rise to an young male gametes called spermatozoids. globular structure that produces motile flagellate Fertilization takes place in the presence of water. a sporophytic plant. generations. Classification Based on the recommendations of ICBN, G. M. Smith (1955) has classified all Pteridophytes into four divisions.

 They are - (1) Psilophyta (3) Calamophyta (2) Lepidophyta (4) Pterophyta Division Psilophyta : It includes fossils and living members. The sporophytic plant consists of underground rhizome, and erect dichotomously branched aerial shoots. True leaves are absent, if present they are small. Leaf, gaps are absent. True roots are absent and rhizoids are present.

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