fi-2 THE STEM 



are very well marked, but they bear onl}- small temporary 

 leaves or none at all. The stems are adapted to functiou 

 as leaves by Ijeing flattened and b_\ retaining the green 

 color necessary for active tuliage. Thus many desert 



53. OpuntcK litipeiHliilii. A I'riukly Fuar Cactus, and 

 tjiMcal desert plant, haviiif; a tliiekeiied stem with 

 green rind, nunierous proteclive spines but no 

 foliage leaves. The n^ots are partly transformed 

 hy tuberons swellings into organs of storage : when 

 planted they grow, like the thickened roots of the 

 Sweet Potato. 



plants like the Cactuses (Fig. 53) liave no foliage leaves. 

 The green rind takes on tlieir function. Tlie total sur- 

 face of these plants is tlius very small comjiared with 

 tlie surface exposed !)y a leafy plant of the same l)ullc, 

 growing in moist climates. The water that the desert 

 plants are able to obtain through their roots in the wet 



