False-colour scanning electron micrograph of a stoma, or pore, on a sepal of the primula flower, Primula malacoides. The stoma appears to be open, but is in fact closed, its inner walls tightly pressed together. Stomata open & close to allow the exchange of gases between plant & atmosphere. Each stoma consists of two guard cells" which control the movement of the pore. The changing shape of the pore is due to the amount of water present in the guard cells. Stomata are most abundant in leaves, where the intake of carbon dioxide through these pores is essential during photosynthesis. Magnification: x270 at 35mm size. Green tint. Reference: MICROCOSMOS, fogure 4.12, page 73."