- stoma
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—stomal, adj.1. Also, stomate. Bot. any of various small apertures, esp. one of the minute orifices or slits in the epidermis of leaves, stems, etc., through which gases are exchanged.2. Zool. a mouth or ingestive opening, esp. when in the form of a small or simple aperture.3. Med. an artificial opening between two hollow organs or between one hollow organ and the outside of the body, constructed to permit the passage of body fluids or waste products.[1675-85; < NL < Gk stóma mouth]
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or stomateAny of the microscopic openings or pores in the epidermis of leaves and young stems.They are generally more numerous on the undersides of leaves. They provide for the exchange of gases between the outside air and the interconnecting air canals within the leaf. A stoma opens and closes in response to turgor pressure within its two surrounding guard cells. Because the inner wall of each of these sausage-or bean-shaped cells is thicker than the outer wall, when they fill with water and become turgid they balloon outward, enlarging the stoma. A drop in carbon-dioxide levels to lower than normal also causes the guard cells to become turgid. Guard cells control excessive water loss from the plant, closing on hot, dry, or windy days and opening when conditions are more favorable.* * *
Universalium. 2010.
