34 



THE ECOLOGY OF STEMS 



photosynthesis. The plants, therefore, are never able to manufacture 

 food so rapidly as can the tropical evergreens. 



(c) Leafless Evergreen Trees and Shrubs.— These plants are still 

 better protected than the sclerophyllous plants because the surface 

 from which water may be lost is so very greatly reduced. Since they 

 have no leaves all food manufacture has to be done by the stems and 



Fig. U.—Ceanothus cuneatus near Palo Alto, California. A broad leaf sclero- 

 phyll. (Photograph by W. S. Cooper.) 



the surface for interchange of gases for this work is also greatly 

 reduced. Such plants cannot manufacture carbohydrates rapidly 

 and so cannot grow rapidly. Examples of leafless evergreen trees 

 are the giant cactus and other large cacti of the American deserts 

 and the large spurges of the African deserts (Fig. 12). 



