30 THE FANTASTIC CLAN 



are translucent and show beautiful colorings: red, orange, 

 yellow, brown, and purple. Generally cactus spines are 

 glabrous, that is, smooth and without hairs, but the spines 

 of some cacti are densely fine-hairy or distinctly hairy; and 

 this can be seen easily with a pocket lens or the unaided eye : 

 their pubescence commonly produces a grayish layer over- 

 lying the true color of the spines beneath. The thorns of 

 Cholla differ from those of other cacti in that they are 

 covered with sheaths which can be removed very easily, 

 and then are not replaced. The significance of these sheaths 

 is not clear, except that they help form a barrier against the 

 intense heat of the sun and the burning desert sands. 



We find, too, that the cacti with most pronounced thorny 

 growth live in the hottest parts of the desert, where the 

 thermometer often registers 130° Fahrenheit during the long 

 summer days and sometimes up to 150°! Their dense layer 

 of spines becomes a shield of lacework, protecting the plants 

 by cutting off over twenty per cent of the light, and reducing 

 the terrible heat by raising the humidity within the network 

 of spines, which in turn reduces evaporation from the plant. 

 If it were not for their thorns and sheaths cacti would be 

 scalded by the burning temperatures of even one summer 

 day in the great desert amphitheater of the sun. Being 

 resinous, cactus thorns are very inflammable, and if ignited 

 they all burn to a cinder before the fire ceases, for one cluster 

 of spines will set others aflame and so the fire sweeps over 

 the entire plant, rapidly changing the beautifully colored, 

 symmetrical and translucent spines into ugly charred masses. 



The cactus is encased in a thick cuticle which is continuous 

 over the whole surface of the plant, except at the numerous, 

 small, rounded or oval areas of growth called areolas. In 

 the cactus all growth, of leaves, spines, spicules, flowers, and 

 even roots (in the case of cuttings) and branches, takes place 

 from these areolas, which are truly areas or centers of 



