Pteridophyte Life Cycle & Alternation — NEET Biology

These gametophytes require cool, damp, shady places to grow. Because of this specific restricted requirement and the need for water for fertilisation, the spread of living pteridophytes is limited and such plants are restricted to narrow geographical regions. The gametophytes bear male and female sex organs called antheridia and archegonia, respectively. Water is required for transfer of antherozoids – the male gametes released from the antheridia, to the mouth of archegonium. Fusion of male gamete with the egg present in the archegonium result in the formation of zygote. Zygotes thereafter produce a multicellular well-differentiated sporophyte which is the dominant phase of the pteridophytes. In majority of the pteridophytes, sporophytes are differentiated into true root, stem and leaves. These sporophytes bear sporangia, which are subtended by leaf-like appendages called sporophylls. In some species, sporophylls may form distinct compact structures called strobili or cones (e.g., Selaginella, Equisetum). The sporangia contain spore mother cells, which give rise to meiospores. In some pteridophytes, the spores are of similar kinds; these are called homosporous. Green like Selaginella and Salvinia which produce two kinds of spores, macro (large) and micro (small) spores; are known as heterosporous. The megaspores and microspores germinate and give rise to female and male gametophytes, respectively. The extent to presence to absence of cambial activity, secondary growth is also variable. For variable periods. The development of the zygotes into young embryos take place within the female gametophytes, thus vent is a precursor to the seed habit considered an important step in evolution.