Very different types of plants with almost no common characters are included under the name of xerophytes. When plants are grown under desiccating conditions there are always a decrease in the dimensions of all cells, increase in number of stomata per unit area, a more compact network of veins in the leaf, denser hair covering, thicker cuticle and wax covering, and very often an increased development of palisade tissue and a decreased development of spongy tissue. These changes create conditions favorable to increased photosynthesis and in many instances to increased transpiration. Experimental evidence shows that many xerophytes have very high rates of transpiration. It is not, however, the rate of transpiration when an abundant water supply is present, but the capacity to restrict water loss to a minimum in time of drought, that characterizes the water utilization of xerophytes. When wilting occurs water loss is much less in xerophytes than in meso-phytes because the former have a much lower rate of cuticular transpiration. The essential quality of the xerophyte is drought resistance, and hence xerophytes are defined as plants of dry habitats which are able to decrease the transpiration rate to a minimum under conditions of water deficiency.