no Field, Forest, and Wayside Flowers 



dried out, and Nature guards against this by ex- 

 posing the least possible proportionate surface to 

 the rays of an ardent sun. The plant substance, 

 instead of being spread out into a great number of 

 thin, flat leaves, is collected into a solid mass, al- 

 most globular in some varieties, and this living 

 lump is covered with a skin, which is richly col- 

 ored with chlorophyll, and acts as one all-enfold- 

 ing leaf. 



The real leaves, superseded in their original 

 work, have become converted into spines or 

 prickles, and act as a deterrent to vegetarian ene- 

 mies. 



A member of the widely-differing family of the 

 spurges, which lives on dry ground under an Af- 

 rican sun, has adopted like habits. Its branches 

 are succulent, spiny prongs, whose surfaces contain 

 chlorophyll, and the plant, when not in bloom, 

 might be mistaken for one of the many varieties of 

 cactus, while the exigencies of the South African 

 climate have driven a native milkweed to do as 

 the cactuses do. In all three of these plants the 

 vegetable substance is condensed into a mass, the 

 inner tissues are full of juice, the bark is converted 

 into an all-enfolding leaf, and the plant body is 

 protected from thirsty vegetarians by thorns, hairs, 

 or prickles (Fig. 22). 



