RELATION OF WATER TO THE PROTOPLASM 65 



water. The epidermis of certain parts frequently subserves 

 this purpose, and many plants possess a considerable 

 development of aqueous tissue, variously disposed, which 

 forms a similar storehouse. The cells of this tissue contain 

 little else than water, and thus serve to supplement the 

 vacuoles of the ordinary cells. In plants that inhabit dry 

 arid soils such as sandy deserts there are often other 

 adaptations relating to water storage. Such plants are 

 often covered with large bladder-like hairs which hold a 

 considerable quantity of liquid. Plants which are exposed 

 to conditions threatening too copious evaporation are gene- 

 rally furnished with a very prominent cuticle tending to 

 check undue escape. 



