Androecium and gynoecium are involved in sexual reproduction. Androecium is the male reproductive part made up of anther and filament whereas gynoecium is the female reproductive part made up of stigma, style and ovary. Reproduction in flowering plants begins with pollination, the transfer of pollen from anther to stigma on the same flower or to the stigma of another flower. Once the pollen grain lodges on the stigma, it germinates and a pollen tube grows from the pollen grain to the ovule. Two sperm nuclei then pass through the pollen tube. One of them unites with the egg nucleus and produces a zygote. The other sperm nucleus unites with two polar nuclei to produce an endosperm nucleus. The fertilized ovule develops into a seed.