(1) Once pollen grain spreads on the stigma, it produces a pollen tube.
This process is called the germination of the pollen grain.
(2) The pollen tube penetrates the style and reaches the ovary.
(3) The male nucleus is transferred through this pollen tube.
(4) Finally, a fusion of male and female nuclei takes place inside the ovary. The zygote develops into an embryo and the embryo undergoes mitotic cell division to form seeds.
(5) The process of fusion of male and female gametes (to form a zygote) is called fertilization.