haploid microspores -> (mitosis) pollen grain
with 2 sperm + tube cellhaploid megaspore -> (mitosis) embryo sac
with 8 nuclei.
Pollination occurs when pollen grains make contact with the stigma (silks)
and develop pollen tubes that grow toward the embryo sac.
One sperm unites with the oocyte nucleus and the other unites with two endosperm nuclei.
This double fertilization produces a diploid zygote nucleus and a
triploid endosperm nucleus.