transpiration, physiological process whereby water taken up from a vine’s roots is evaporated through the leaves, important in preventing the vine from overheating in sunny weather. Water and dissolved elements move in the so-called transpiration stream through the woody part of the vine called the xylem. The xylem fluid also contains relatively large amounts of amino acids, especially glutamine, organic acids, especially malic, and small amounts of sugars. Total water loss from a vineyard is called evapotranspiration, and this includes transpiration from the vines and also any weeds or cover crop present, plus evaporation from the soil surface.
