A pollen grain on maturation undergoes one unequal mitosis to form a smaller generative cell and a larger vegetative cell. In 60% angiosperms, pollen grain is liberated at this two-celled stage. Thus, a mature pollen grain consists of 2 cells. In the remaining species, the generative cell divides mitotically to give rise to the two male gametes before pollen grains are shed (3-celled stage).