What process happens when pollen falls on a flowers pistil?

Pollination brings together the gametes of a flower and it occurs when

a pollen grain of the right kind lands on the stigma of the pistil. Each pollen

forms a tube that grows down through the pistil and reaches the ovule in

the ovary. One of the nuclei in the pollen tube unites with the egg nucleus

in the ovule to form a zygote. The other sperm nucleus combines with

another bigger nucleus in the ovule which develops into the endosperm.