Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. Water is necessary for plants but only a small amount of water taken up by the roots is used for growth and metabolism. The remaining 99-99.5% is lost by transpiration. Leaf surfaces are dotted with pores called stomata, and in most plants they are more numerous on the undersides of the foliage.