When ripe pollen from an anther of the same kind of flower catches on the stigma, each pollen grain sends out a tiny threadlike tube called pollen tube. The tube grows down through the style, reaches the ovary of a pistil and pierces one of the ovules in the ovary. A male gamete fuses with a female gamete in the ovule.This process is called fertilization.
Each ovule must receive the contents of the pollen tube before it can develop into a seed. It usually takes the tube from two to five days to reach the ovule, but the time may vary from a few hours to six months.