Pollen And Ovules

Pollen And Ovules

Seed plants probably evolved from fern-like ancestors. They do not show the marked alternation of generations that is typical of more primitive land plants. In spermatophytes the sexual (gametophyte) generation is telescoped into a tiny part of the life cycle. Most of the more primitive plants are homosporous which means that all their spores look the same but a few are heterosporous producing larger female spores and smaller male spores. Seed plants are heterosporous; pollen grains give rise to the male gametes and an ovule contains the female spore. This picture shows pollen-producing male catkins. [CH] {EB}