Morphology of a pollen grain - a taste of things to come.

Pollen is made up of a durable microspore wall composed of sporopollenin and an enclosed microgametophyte. Various vectors can carry pollen grains away after their release from the microsporangium. If a pollen grain lands near an ovule, it will extend a tube to discharge one or more sperm cell into the female gametophyte to fertilize it. The use of resistant pollen grains to transmit genetic material necessary for the fertilization process is a terrestrial adaptation that helped plants achieve a greater success on land and a high diversity. The two figures in the following pages will illustrate the differences between the life cycle of gymnosperms (cycads, ginkgo, gnetophytes and conifers) and angiosperms (flowering plants).