if the water potential (or strictly, water vapour potential) inside a leaf is higher than outside, the water vapour will diffuse out of the leaf down this gradient. this loss of water vapour from the leaves is called transpiration, and the water vapour diffuses through the open stomata. transpiration is natural and inevitable for plants; a significant amount of water is lost through this process. however, it is vital that plants living in dry conditions are adapted so as to decrease the size of the open stomata, lower the rate of transpiration, and consequently reduce water loss to the environment. without sufficient water, plant cells lose turgor. this is known as plasmolysis. if the plant loses too much water, it will pass its permanent wilting point, and die.