/ stoʊmə /
ETYM New Lat., from Greek stoma a mouth.
A minute epidermal pore in a leaf or stem; SYN. pore.
Mouth; orifice; breathing pore of plants.
In botany, a pore in the epidermis of a plant. Each stoma is surrounded by a pair of guard cells that are crescent-shaped when the stoma is open but can collapse to an oval shape, thus closing off the opening between them. Stomata allow the exchange of carbon dioxide and oxygen (needed for photosynthesis and respiration) between the internal tissues of the plant and the outside atmosphere. They are also the main route by which water is lost from the plant, and they can be closed to conserve water, the movements being controlled by changes in turgidity of the guard cells.
Stomata occur in large numbers on the aerial parts of a plant, and on the undersurface of leaves, where there may be as many as 300,000 per square inch.