Transpiration

In plant-water relations studies, the dominant processes are the uptake of huge quantities of water from the soil, its translocation through the plant and its subsequent loss from the aerial parts to the surrounding atmosphere in the form of water vapour through transpiration. Out of the total water absorbed by the plant during a growing season, about 99 per cent is lost to the atmosphere in the form of water vapour and only 1 per cent is retained by the plant. Out of this 1 per cent, roughly 0.9 per cent is retained as free water within the tissue and about 0.1 per cent enters into the plant's metabolism as a reactant in chemical reactions (e.g., photosynthesis). The process of water loss in the form of vapour from the leaf surfaces of the plant is called transpiration.