Pollen grains are an outrageous invention of the seed plants, which first appeared over 300 million years ago. Pollen frees the seed plants from dependence on standing water for [F]ertilization, which is needed by the spore-reproducing plants like ferns. The distinction is similar to the difference between amphibians vs. reptiles. Pollen is produced in the male organs of the flowers - anthers. Pollination occurs when pollen is transfered from the anthers to the female organs by wind (anemophyly) or by animals (zoophyly). If the female stigma is receptive to a pollen grain, the pollen produces a pollen tube, which grows through the female tissue to the egg, where fertilization takes place by the sperm nucleus.