transpiration

transpiration
/tran'speuh ray"sheuhn/, n.
1. an action or instance of transpiring.
2. Bot. the passage of water through a plant from the roots through the vascular system to the atmosphere.
[1545-55; TRANS- + L spiration-, s. of spiratio breathing (spirat(us), ptp. of spirare to breathe + -ion- -ION); perh. directly < F or NL]

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Loss of water from a plant, mainly through the stomata (see stoma) of leaves.

Darkness, internal water deficit, and extremes of temperature tend to close stomata and decrease transpiration; illumination, ample water supply, and optimum temperature cause stomata to open and increase transpiration. Its exact significance is disputed; its roles in providing the energy to transport water in the plant and in aiding dissipation of the sun's heat (by cooling through evaporation of water) have been challenged. Since stomatal openings are necessary for the exchange of gases, transpiration has been considered by some to be merely an unavoidable phenomenon that accompanies the real functions of the stomata.

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▪ botany
      in botany, a plant's loss of water, mainly through the stomates of leaves. Stomates consist of two guard cells that form a small pore on the surfaces of leaves. The guard cells control the opening and closing of the stomates in response to various environmental stimuli. Darkness, internal water deficit, and extremes of temperature tend to close stomates and decrease transpiration; illumination, ample water supply, and optimum temperature open stomates and increase transpiration. The exact significance of transpiration is disputed; its roles in providing the energy to transport water in the plant and in aiding in heat dissipation in direct sunlight (by cooling through evaporation of water) have been challenged. Stomatal openings are necessary to admit carbon dioxide to the leaf interior and to allow oxygen to escape during photosynthesis, hence transpiration has been considered by some authorities to be merely an unavoidable phenomenon that accompanies the real functions of the stomates.

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Universalium. 2010.

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