Pea flower pollination. Coloured scanning electron micrograph (SEM) of pollen grains (ovals) on the stigma of a garden pea flower (Pisum sativum). The pollen grains, which contain male genetic material, have become trapped by the stigma's papillae (hair-like structures, green). The stigma is part of the female reproductive structure (pistil), which is formed from one or more carpels. Each carpel consists of a stigma, a style and an ovary (not seen). If the female sex cells (ovules) in the ovary become fertilised by the pollen grains' male sex cells, the carpel may ripen to produce a fruit containing seeds.