question_answer 33)

    The heterosporous pteridophyte show certain characteristics, which are precursor to the seed habit in gymnosperms. Explain.

Answer:

                  Heterospory, i.e., production of two types of spores smaller microspores and larger megaspore was first reported in Selaginella a pteridophyte. In Selaginella, the smaller microspores are destined to produce male gametophytes and the larger megaspores to female gametophyte. The male gametophyte produces male gametes, whereas the female gametophyte produces archegonia and also provides nourishment to the developing embryo. The phenomenon of heterospory, thus lead to the reduction of gametophyte, in situ germination of spores, retention of mega gametophyte in the mega sporangia and finally to the seed development. Thus, the heterospory in Selaginella forms the base for seed habit development in gymnosperms.