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1. Botany an epidermal pore, present in large numbers in plant leaves, that controls the passage of gases into and out of a plant
2. Zoology anatomy a mouth or mouthlike part
3. Surgery an artificial opening made in a tubular organ, esp the colon or ileum



a slitlike opening in the epidermis of aboveground organs of plants. The stoma is bordered by two guard cells, which are usually bean-shaped. The walls of the guard cells that face the stoma are thick, while the opposite walls are thin. The stoma leads to a large intercellular space, the substomatal cavity. The stoma is often surrounded by two or more cells that differ in shape from ordinary epidermal cells.

Stomata are found in the epidermis of all aboveground parts of the plant containing chlorophyll but are especially numerous in leaf epidermis (100–300 per sq mm). They regulate the exchange of gas and water vapor between the atmosphere and the cells of the plant by increasing and decreasing in width. Stomatal movement is effected by changes in the turgor of the guard cells. When turgor is increased, the thin parts of their walls stretch and are drawn away from the stoma. The walls that face the stoma are distended in the same direction, and the stoma opens. When the turgor of the guard cells decreases, the stoma closes. Change in the turgor of the guard cells occurs as a result of reversible conversion of starch, which is osmotically inactive, into osmotically active sugars. However, according to some data, potassium ions play an important, possibly leading, role in regulating the turgor of the guard cells. Scientists are currently investigating these data with the intention of formulating a new hypothesis of the mechanism of stomatal movement.

At night, the stomata of most plants are closed, and gas exchange and transpiration are minimal. During the day, when the weather is fair, the stomata are open. Carbon dioxide gas readily enters the internal tissues of the plant, and oxygen formed as a result of photosynthesis is released with water vapor into the atmosphere.



A small opening or pore in a surface.
One of the minute openings in the epidermis of higher plants which are regulated by guard cells and through which gases and water vapor are exchanged between internal spaces and the external atmosphere.
References in periodicals archive ?
Transpiration is the loss of water through stomates. Humidity around the leaves can reduce the rate of water loss from a plant, thus reducing the water uptake in the roots.
Key words: Fagaceae, leaf venation pattern, Quercus, stomates.
(1998), indicated that it is necessary to maintain high relative humidity and low light intensity until plants have adequately developed stomates and cuticle.
An interesting example of all three patterns is the occurrence of clustered stomates on leaves in some Begonia cultivars (Figure 1).
A similar situation occurs al Antifreeze Pond, with stomates and macrofossils indicating local spruce, but low (< 5%) pollen frequencies suggesting otherwise (Vermaire, 2005).
Leaves of Cakile species have been reported to range from 0.5-1.5 mm in thickness, have stomates on both leaf surfaces, and have undifferentiated parenchyma (Rodman 1974).
Increasing C|O.sub.2~ concentration in the atmosphere around a leaf causes the stomates to partially close, which reduces the transpiration or rate of loss of water from the leaf.
For example, under drought conditions, ABA levels in leaves increase, and exogenous application of ABA induces closure of stomates, the pores in leaves through which gases and water pass.
complex because of the presence of stomates, trichomes, and veins, as
Anatomical studies showed differences in size and shapes of prickles, short cells, silica bodies, micro hairs with basal and distal cells, hooks, stomates and long cells of Paniceae species.
Others obtain entry into plants by insect vectors or can simply enter through stomates. Still others are able to attack tissue directly and soften it or are otherwise able to break through epidermal tissue.
These plants should do better under hot, dry conditions because they can close the stomates on their leaves during the day, thereby reducing water use."