question_answer 30)

  Heterospory, i.e., formation of two types of spores? microspores and megaspores is a characteristic feature in the life cycle of a few members of Pteridophyta and all spermatophytes. Do you think heterospory has some evolutionary significance in plant kingdom?

Answer:

                  Heterospory is production of spores of two different sizes and sexes by the saprophytes of land plants. Two types of spores are produced by heterosporic plants. Small spores are microspores which germinate into male gametophyte and large spores are macrospores which develop into female gametophyte. In evolution of plants Pteridophyta are intermediate between bryophytes and gymnosperms. All bryophytes are homosporous and all gymnosperms are heterosporous. This condition is advanced as sexual dimorphism result in cross fertilization. Primitive or earlier Pteridophyta are homosporous later pteriodophytes are heterosporouse.g., Dryopteris, Pteris  homosporous Selaginella, Salvinia-heterosporous.