The generative cell usually divides to form two sperm cells during migration down the pollen tube. An embryo sac develops in the ovule, and number of nuclei form in the embryo sac by division from a single cell. The second sperm cell fuses with two polar nuclei to form the endosperm , which is nutritive tissue used by the developing embryo . The entire ovule develops into the seed . If there is more than one ovule within the ovary, each must be fertilized independently of the others.
Pollination requires a vector to carry the pollen from the anther to the stigma.
These can include wind, water, insects and birds. Grasses and gymnosperms use wind pollination. These plants typically do not have showy floral parts, fragrances, or nectar . Their stigmas are large, and their stamens are well-exposed. Each flower has only one ovary with a single ovule, but many flowers are packed into each inflorescence.