transpiration defined in 1951 yeartranspiration - transpiration;
transpiration - Loss of water-vapour by land plants. Occurs mainly from leaves and differs from simple evaporation in that it takes place from living tissue and is therefore influenced by physiology of plant. Transpiration takes place chiefly through stomata and to a much less extent through the cuticle. Its significance is not completely understood. So long as stomata are open during interchange of gases between plant and atmosphere in photosynthesis and respiration, loss of water-vapour to the atmosphere must occur, i.e. for a healthy plant transpiration is inevitable. When it is excessive it is often harmful to the plant, causing wilting and even death. On the other hand there seems little doubt that it facilitates the upward movement of mineral salts in the xylem in the transpiration stream, though there is no consistent relationship between amount of water transpired and salt taken up; and it may also be of importance in preventing overheating in direct sunlight. transpiration stream. Flow of water through plant as a result of loss of water by transpiration. Diffusion pressure deficit (DPD) of cells of transpiring leaves causes osmotic withdrawal of water from xylem elements causing a tension (negative pressure) in water in xylem that exerts an upward pull (transpiration pull) through cohesion of water molecules. Tension is transmitted to roots from which water is withdrawn, aided by root pressure. This then leads to increased DPD of root cells and increased water absorption by roots.
near transpiration in Knolik
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