Plant pores. Coloured scanning electron micrograph (SEM) of stomata (dark green) on a pistil. Other plant cells are seen around the stomata. Stomata are pores that regulate the exchange of gases and water vapour into and out of the plant. The highest concentration of stomata is found on the leaves of a plant, but they are also found elsewhere, such as the pistil in this case. A pistil, part of a flower, is part of the female reproductive structure of a plant. These stomata are from a chameleon plant (Houttuynia cordata).