The female gametophyte is the embryo sac . At the opposite end are 3 antipodal cells. The placement of pollen onto the stigma of a carpel. Some plants use wind to disperse pollen. Other plants interact with animals that transfer pollen directly between flowers.
Most monoecious angiosperms have mechanisms to prevent self-pollination.
These mechanisms thus contribute to genetic variation in the species by ensuring sperm and eggs are from different plants. The stamens and carpels mature at different times in some species. Structural arrangement of the flower in many species pollinated by animals reduces the chance that pollinators will transfer pollen from anthers to the stigma of the same flower. Other species are self-incompatible . If a pollen grain lands on the stigma of the same flower, a biochemical block prevents the pollen grain from developing and fertilizing the egg.