pollen

Pollination, the process by which pollen grains transfer their male nuclei (gametes) to the ovary of a flower. The pollen grains land on the stigma and form a pollen tube that grows down into the ovary. The male nuclei travel along the pollen tube.

Grains of seed plants that contain the male gametes. In angiosperms (flowering plants) pollen is produced within anthers; in most gymnosperms (cone-bearing plants) it is produced in male cones. A pollen grain is typically yellow and, when mature, has a hard outer wall. Pollen of insect-pollinated plants (see pollination) is often sticky and spiny and larger than the smooth, light grains produced by wind-pollinated species.

The outer wall of pollen grains from both insect-pollinated and wind-pollinated plants is often elaborately sculptured with ridges or spines so distinctive that individual species or genera of plants can be recognized from their pollen. Since pollen is extremely resistant to decay, useful information on the vegetation of earlier times can be gained from the study of fossil pollen. The study of pollen grains is known as palynology.

Certain types of pollen can cause allergic reactions in humans, known as hay fever.