Fertilisation:

1. Fertilisation is the process of fusion of male and female gametes. For fusion of male and female gametes, pollen grains have to reach the surface of the stigma.
2. Pollen grains received by stigma germinate and give rise to pollen tubes. Only one pollen tube finally reaches the embryosac.
3. This tube will have 2 male nuclei, which migrate to the tip of pollen tube at the time of fertilisation.
4. One male gamete approaches the egg and fuses with egg to form a diploid (2n) zygote. This is first fertilisation.
5. The other male gamete reaches the secondary nucleus and fuses with it to form endosperm nucleus which will be triploid (3n). This is second fertilisation in embryosac.
6. In this way, diploid zygote is formed by union of male and female gametes in embryosac of ovary and triploid (3n) endosperm nucleus is also formed during fertilisation. With this fertilisation is completed.