The study of sporoderm morphologya and ultrastructure in gymnosperms (including seed ferns) and angiosperms has been made. Possible paths of evolution in pollen grains, which originated from different seed fern groups has been revealed. Numerous ways of pollen grain specialization which resulted in observed diversity of modern gymno- and angiosperm pollen grains has been followed. These ways are shown in the original scheme of possible evolution of pollen grains in seed plants.
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