Stomata (stŏm′ȧ-tȧ) (in plants). Narrow openings are developed in the epidermis of STOMATA AND LEAF all aërial parts of plants which require and emit gases. (See Aëration.) Gaseous exchanges especially abound in green tissues; hence stomata are chiefly displayed by the foliage-leaves of the higher plants. Each stoma consists of two specially organized epidermal cells, called guard-cells, which are crescentic in surface-view and, being in contact by their concave faces, leave a lens-shaped opening between them. This opening leads into the system of intercellular passageways among the working-cells, and thus provides for a free exchange of gaseous substances between the working-cells and the outside air. The guard-cells change form with the varying amounts of moisture in the air, and so regulate the size of the opening between them. Stomata have been called “automatic gateways” on account of this peculiar power of the guard-cells. See Leaf and Transpiration.