transpiration

Loss of water from a plant by evaporation. Most water is lost by diffusion of water vapour from the leaves through pores known as stomata to the outside air. The primary function of stomata is to allow gas exchange between the plant's internal tissues and the atmosphere. Transpiration from the leaf surfaces causes a continuous upward flow of water from the roots via the xylem, which is known as the transpiration stream. This replaces the water that is lost, and allows minerals absorbed from the soil to be transported through the xylem to the leaves. This is important because many plant cells need the minerals as nutrients.