Pollen Pollen Pollen is a fine to coarse powdery substance comprising pollen grains which are male microgametophytes of seed plants, which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophytes during the process of their movement from the stamens to the pistil of flowering plants, or from the male cone to the female cone of coniferous plants. If pollen lands on a compatible pistil or female cone, it germinates, producing a pollen tube that transfers the sperm to the ovule containing the female gametophyte. Individual pollen grains are small enough to require
Pollen tube grains are deposited in the micropyle of the ovule of a female cone or megastrobilus, where they mature for up to a year. In conifers and Gnetophytes the pollen germinate to produce a pollen tube that penetrates the megasporangium or nucellus carrying with it sperm nuclei that are transferred to the egg cell in the developing archegonia of the female plant. The female sporophyte must recognize the pollen stuck to the stigma. Often, only pollen of the same species can successfully grow and outcrossed pollen is more successful in growing. With self-incompatibility systems, outcrossed pollen grows and outcompetes self pollen.