Transpiration

Transpiration, loss of water by evaporation from the aerial parts of plants. Considerable quantities of water are lost in this way, far more than is needed for the upward movement of solutes and for the internal metabolism of the plant alone. Transpiration is necessary for photosynthesis: In order to obtain sufficient carbon dioxide from the air, considerable areas of the plant's wet surface have to be exposed. But as a result, much water is lost through evaporation.