Bellflower pistil. Coloured scanning electron micrograph (SEM) of the pistil of a bellflower (Adenophora sp.). The pistil is the female reproductive part of a flower. In this plant it consists of fused carpels. The carpels contain the ovules, the female gametes (sex cells). The ovaries are fertilised by pollen grains, the male gametes. The pores on the surface of the carpel are stomata. They are the site of gaseous exchange, or respiration. Carbon dioxide enters the plant for use in photosynthesis, and waste oxygen leaves the plant via the stomata. Magnification: x60 when printed at 10 centimetres tall.