The embryo and protective layers are called a seed. The fragrance, nectar and color of flowers attract insects, birds and mammals. They carry pollen to the stigma resulting in pollination. Flowers lacking showy petals, as in many deciduous trees, are usually pollinated by the wind. The structure of the flower often gives clues about the mechanism for pollination.
Most plants are self-fruitful.
Some plants are self-sterile and cannot be fertilized by their own pollen. Pears, plums and some apples are self-sterile. Cross-pollination is the carrying of pollen from one plant to another. Cross-pollination increases genetic variability. Genetic variability means that offspring plants carry the genetic information that may show new physical characteristics not seen in the parent plant.