IS8 



Science of Plant Life 



Fig. Sy. A desert scene in Arizona. 



UoJgion 



duced leaf area or a complete absence of leaves. The stems 

 also may be reduced in size and amount of branching. 



The cactuses represent extreme examples of this type of 

 plant. Leaves are wanting; and the stems are columnar, 

 often ridged and fluted, and always thick and fleshy. The 

 photosynthetic work in cactuses is done by the cortical tis- 

 sue. As the green surface is small compared with the green 

 surface in mesophytic plants, food manufacture is slower 

 and growlh is correspondingly less. Some of the cactuses of 

 Mexico attain heights of 60 feet. The cactus form points 

 clearly to one of the most characteristic features of desert 

 plants ; namely, water storage. A single plant may contain 

 from 15 to 20 gallons of water. As the plant loses moisture 

 so slowly, it may continue to live for several years without 

 an additional supply of water. Other desert plants that 

 accumulate water in the leaves were mentioned on page 58. 



