Plants adapt to dry conditions in a variety of ways, but many respond to dry conditions by storing large quantities of water, which can be used in times of need. For example, cactuses store water in their trunks and stems, while aloe plants store water in their leaves. Additionally, plants that live in dry areas often evolve thick outer cuticles that can help retard the rate of water loss.
Some plants will discard their leaves when the humidity level drops or a drought occurs. When the rains return, the plant will produce more leaves and regain its vigor. This is similar to the annual leaf drop that accompanies some deciduous plants. Contrary to popular thought, deciduous plants drop their leaves in the winter as a response to the lack of water, not the reduced temperatures.
Tree and plant leaves often have small holes on their lower surfaces, called stoma. These openings allow water to escape into the atmosphere, in a process known as transpiration. The reason that plants function this way is to draw water up from the roots. As the water evaporates from the leaves, it creates a suction effect, which draws the water from the ground via the roots.