Plant stomata. Light micrograph of stomata (white) on the surface of a plant. Stomata are pores that regulate the exchange of gases and water vapour into and out of the plant. Guard cells (blue) either side of the opening control this by osmotic pressure; the swelling of the cells causing the them to bow apart from one another, thus opening the pores and accelerating gas exchange. The highest concentration of stomata is found on the leaves of a plant, but they are also found elsewhere. This image was created using an epithelial peel to chemically remove the top layer of the leaf.