Process of (Double) Fertilisation in Flowering Plants
Pollen grains land onto the stigma and adhere to it as a result of the stigma cells secreting a sticky substance.
It absorbs nutrients; and germinates forming a pollen tube; the pollen tube grows down the style to the ovary; deriving nourishment from surrounding tissue.
The pollen tube has a tube nucleus at the tip, and generative nucleus immediately behind it;
As the pollen tube grows downwards into the ovary the generative nucleus divides mitotically, to give rise to two male nuclei; which represent the male gametes; the pollen tube penetrate the ovule/embryo sac through micropyle.
When the pollen tube enters the embryo sac, the tube nucleus breakdown/ disintegrates; leaving a clear passage for the entry of the male nuclei.
The two male nuclei then enter into the embryo sac; where one male nucleus fuses with the egg cell nucleus; to form a diploid zygote; which develop into an embryo.
The other male nuclei fuse with the two polar nuclei; to form a triploid nucleus/ primary endosperm nucleus; which later becomes the endosperm.
This (type of fertilization) is called double fertilization;