Definitions for "Pollen grain"
The microspore of a seed plant, haploid cells that comprise of give rise to the male gametophyte (microgametophyte)
The male gametophyte in higher plants.
Pollen grains are produced by flowering plants, gymnosperms and cycads as a way of reproducing even in areas where water is not easily available. As such, pollen represents an advanced feature of adapting to a life on land. Individual pollen grains are tiny, with almost no reserves inside them; essentially they are 'male' genetic material wrapped in two membranes. The outer membrane is smooth and rounded in wind-pollinated plants, and often highly sculpted and shaped in insect-pollinated plants. Pollen grains represent the vestiges of a highly reduced male gametophyte generation.
Keywords:  particle, single
A single particle of pollen.