YOUNG BRANCH WITH LEW ES 



The little conical buds shown on the above shoot, which is 

 photographed natural size, are the true leaves of the 

 cactus. They are soft in texture, and fall off before 

 the branch has attained great size. They are mere 

 vestiges of the leaves that the cactus had at some much 

 earlier stage in its evolution, and at present they seem 

 to serve no useful purpose. (Fig. 6.) 



and sometimes closely covering square 

 rods of surface like a coarse, ^Yoolh■ 

 blanket. (Fig. 3.) 



Although the "polar bear cactus" 

 does not resemble its namesake in having 

 exclusive possession of its peculiar 

 environment, it may be a good example 

 of adaptation. For, although two or 

 three naked species grov^ even to so 

 great an altitude as that of the summit 

 of the Pass of La Raya, that is, at an 

 elevation of more than 14,000 feet, 

 they certainly show no such comfortable 

 prosperity as the shaggy form. The 

 naked species are relatively scarce and 

 small. The Andine cactus flora would 

 attract no attention from the traveler 

 if the shaggy species were not there. 



A NAKED FORM 



One of the naked cacti is so closely 

 related to the shaggy form as to be 

 referred to the same species, Opuntia 

 fioccosa, by Dr. J. N. Rose, of the 

 U. S. National Museum, the best au- 

 thority on this group of plants. The 



difference may lie onh" in the length of 

 the spicules, which are as short as in 

 ordinary cacti. The existence of this 

 naked form is another evidence that 

 the shaggy coat is not indispensable, 

 but the unclothed plants are much less 

 common, and this indicates that the 

 hair is distinctly advantageous. The 

 naked plants appeared distinctly 

 shrunken even at the beginning of the 

 Peruvian winter, like our native Opuntia 

 vulgaris, which grows as far north as 

 Washington, D. C.; but the hairy Peru- 

 vian cacti were still plump and succu- 

 lent, as in the specimen shown in 

 Fig. 5, representing a photograph 

 taken at Araranca, on the 13th of 

 April, 1915. 



According to Weberbauer this species 

 extends northward from the Titicaca 

 basin to about 10° south latitude. 

 Another white hairy species, Opuntia 

 lagopus, is found only in the region of 

 Lake Titicaca. Weberbauer has pub- 

 lished a photogra])h of the two species 

 growing together in the vicinity of Poto, 



117 



