After pollination the pollen grains drop on the sticky stigma of the flower.
They germinate here producing two male gametes and a long pollen tube.
The male gametes travel through the pollen tube till they reach the embryo sac.
Here the male gametes are released by bursting the pollen tube. One male gamete unites with the egg cell to form zygote while the second male gamete unites with two polar nuclei forming endosperm.
In this way because two nuclei participate in the fertilization process, therefore it is called double fertilization.
