Each young ovule within an ovary contains a megasporocyte that undergoes meiosis to produce four haploid megaspores. Three of these usually disintegrate, and one divides mitotically and develops into a female gametophyte, also called and embryo sac. The embryo sac contains seven cells with eight haploid nuclei. Six of these cells including the egg cell, contain a single nucleus each , and a central cell has two nuclei, called polar nuclei. Each pollen sac, or microsporangium, of the anther contains numberous microsporocytes, each of which undergoes meiosis to form four haploid microspores.
Every microspore develops into an immature male gametophyte, also called a pollen grain.
The anther sacs split open and begin to shed pollen. Pollen grains are transferred to the stigma by a variety of agents, including wind, water, insects, and other animal pollinators. Next,the generative cell divides to form two nonmotile male gametes called sperm cells. The sperm cells move down the pollen tube and are discharged into the embryo sac. Both sperm cells are involved in fertilization.