Scanning electron micrograph of pollen grains and the stigma of a turnip flower, Brassica campestris. The picture shows the female stigmatic surface as the green background. The (pale orange) pollen grains, about 30microns long, have a patterned outer wall containing sporopollenin. The central grain has germinated to produce a pollen tube (light brown) which has penetrated the surface of the stigma. The tube contains two male gametes (sperm), and grows downwards until it reaches the female ovary, that contains many ovules (eggs). Fertilisation consists of one of the sperm fusing with one nucleus in an egg, to intitiate growth of an embryo. The other sperm fuses with two nuclei in the egg, resulting in the formation of endosperm. Endosperm is the nutritious tissue that feeds the mature embryo after the seed germinates, until the new plant develops leaves and photosynthesis can begin