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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
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



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.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


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.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Unlike photosynthesis response to soil moisture stress, stomatal conductance ([g.sub.s]) and transpiration rates declined linearly in all corn hybrids with declining soil moisture content (Fig.
Stomatal densities and plant morphometry: We tagged all plants within each plot, and for each plant, we measured basal stem circumference with a standard measuring tape, taking measurements just above the first pair of aerial roots.
Table 1: Stomatal index Number of stomata Number of Stomatal index (%) epidermal cell Upper surface 2 10 16.6 Lower surface 4 12 2 Table 2: Results of phytochemical screening of cola herb Test Result Saponin + Tannin + Coumarin + Flavonoid + Table 3: Components of volatile oil of A.
Stomatal conductance at GS6 was not found to be significantly different among N-fertility rates, hybrids, or years.
Reese et al., "A toolbox of genes, proteins, metabolites and promoters for improving drought tolerance in soybean includes the metabolite coumestrol and stomatal development genes," BMC Genomics, vol.
Stomatal conductance and net photosynthesis are inhibited by moderate heat stress in many plant species due to decrease in activation state of rubisco (Monson et al., 1982).
In the current study, transpiration rates and stomatal conductance were high at the [A.sub.max] (Table 1), which is typical of sun plants.
Stomatal density, LMA, water content, chlorophyll per unit mass, and leaf lifespan were correlated with the light environment in a small-scale spatial gradient from the edge to the interior of a small forest stand.
distorta [P.sub.N] and [g.sub.s] are higher compared to other mountain species growing at lower altitudes (Woodward, 1986) confirming the general trend for which plants tend to maximize net photosynthesis and stomatal conductance with increasing altitude in relation to the shorter growing season (Gornall & Guy, 2007).
The effect of these three type of salinity on the leaves thickness, leave area, succulence, stomatal conductance and length of C.