Fertilization, the process leading to the production of seeds and fruits, occurs after compatible pollen has been transferred to the stigma of a flower. A pollen grain contains two cells. One of these germinates and develops into the pollen tube, a structure that quickly grows through the style and enters an ovule. The other pollen cell divides into two sperm, which move through the pollen tube. One sperm fertilizes the egg in the ovule; the other unites with another cell in the ovule and develops into the endosperm, the food supply which will nourish the developing embryo and, in some plants, the germinating seedling as well.

DEVELOPMENT OF FRUIT

Fertilization stimulates other changes. A seed coat forms around the developing embryo and endosperm, creating the seed. Around the seed, the ovary wall forms a layer called the pericarp, which in most species develops into the fruit. When the seed is mature--ready for dispersal--the fruit may be fleshy and soft, as in the case of peaches or cherries; or it may be dry, like an acorn or dried pea pod.

The role of a fruit is to protect the seed until maturity; it often helps to spread seeds, as well. For example, the fruits of a maple tree have winglike structures that help them spin through the air; the fruits of a dandelion have a tiny parachute that disperses the seed on the wind. And of course, birds and animals eat many fruits (fleshy and otherwise), scattering the seeds far and wide.