Inside the anther there are pollen mother cells. By meiosis four pollen grains are produced from each pollen mother cell. Each pollen grain contains two coverings, the outer coating is called exine and the inner one is called intine. In the exine there is a pore named germ pore Nucleus of the pollen grain undergoes mitotic division and forms tube nucleus and generative nucleus. Usually pollination occurs at this bi-nucleated condition.
Fig: Stages of development of male gametes
As a result of pollination, the pollen grains become attached to the stigma and a pollen tube is developed from the pollen grain. The tube gradually makes its way down into the ovary through the style. The tube nucleus enters the pollen tube followed by the generative nucleus. The generative nucleus undergoes mitotic division and form two male reproductive cells or male gametes or sperms. The male gametes are haploid.