Anthers on stamens -> (meiosis) 4 haploid microspores -> (mitosis) pollen grain with 2 sperm + tube cell
Ovaries in pistils -> (meiosis) 1 haploid 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.