Scanning electron micrograph of self-pollination in a chickweed flower, Stellaria media; its foreground petals removed to show the sexual organs. The 1mm wide bulbous female gynoecium (below centre) contains the ovaries; at its tip are 3 styles tipped with feathery stigmas (brown). 5 male stamens are present; 2 with yellow nectaries visible at the base. At their tips paired anthers are shedding pollen (red). Shed pollen is polygonal in shape - best seen at picture left. As it contacts a stigmatic surface, pollen germinates. It imbibes water, expands and becomes spherical (above picture centre). It then produces a pollen tube that grows down through the stigma to the ovaries, conveying sperm cells to fertilise the ovarian eggs. Germination only occurs if the pollen and stigma are compatible. Some plants self-pollinate, as here. Others cross-pollinate, with pollen from a different plant.