Moisture is lost via the stomata of a leaf, in an evaporation process known as transpiration in the case of trees and plants.
The water evaporates via the so-called stomata or leaf pores, which are usually found on the underside of a leaf.
Trees and plants evaporate water in order to create a continuous upward sap flow, enabling them to eventually get the transported salts into the leaf.
Evaporation then disappears by means of diffusion via the leaf stomata to the air around the plant. The degree of evaporation (evaporation rate) is mainly determined by the relative humidity.