OPUNTIA. 87 



at hand, they had the appearance of large, rounded, flattened cushions, some five or six feet in diam- 

 eter, and a foot high, covered with dense masses of floss silk that glistened with a silvery lustre. The 

 unwary stranger who should be tempted to use one of these for a seat would suffer from the experi- 

 ment. The plant is of the cactus family, and the silky covering conceals a host of long, slender, 

 needle-like spines, that penetrate the flesh, easily break, and are most difficult to extract. Unfor- 

 tunately, the living specimen which I sent to Kew did not survive the journey. 



Dr. Rose found the plant very abundant in the Andes from 3,600 to 4,260 meters 

 altitude, while others have reported it as high as 4,570 meters altitude. It is very common, 

 forming everywhere great, conspicuous, usually white mounds. Dr. Rose also found it 

 quite common between Cuzco and Juliaca, in southwestern Peru. 



Mr. O. F. Cook, in the Journal of Heredity (8: 113. 1917), who has named this plant 

 the polar bear cactus, wrote of it as follows: 



Many exposed slopes on the bleak plateaus of the high Andes are dotted with clumps of pure 

 white cacti that look from a distance like small masses of snow. On closer view, the shaggy white 

 hair of these cacti make them appear like small sheep or poodle-dogs, or like reduced caricatures 

 of the denizens of the arctic regions. We are so accustomed to think of cacti primarily as desert 

 plants, peculiarly adapted to hot, dry deserts, that they seem distinctly out of place on the cold 

 plateaus of the high Andes of southern Peru. 



While most of the plants are covered with long white hairs, plants without hairs 

 are not uncommon. These naked plants, which are characteristic of the whole clump 

 or colony, appear at first sight very unlike the other forms, but they grow in the same region 

 and have the same kind of flowers and fruits. In cultivated plants few hairs are developed. 

 The variety denudata Weber seems to be only one of these naked forms. 



Opuntia involuta Otto (Forster, Handb. Cact. 505. 1846) was not published, but was 

 given as a synonym of this species. It was used the year before (Salm-Dyck, Allg. Gar- 

 tenz. 13: 388. 1845) as a synonym of 0. vestita. 



Illustrations: Engler and Drude, Veg. Erde 12: pi. 14; Monatsschr. Kakteenk. n: 41, 

 44, these last two as Opuntia hempeliana; Journ. Heredity 8: f. 3 to 8. 



Plate xni, figure 2, is from a photograph taken by Mr. O. F. Cook in the high moun- 

 tains of eastern Peru. Figure 101 is from a photograph of a fragment of the plant col- 

 lected by Dr. Rose in 1914, at Araranca, Peru. 



57. Opuntia lagopus Schumann, Gesamtb. Kakteen Nachtr. 151. 1903. 



Plants cespitose, growing in compact mounds; joints stout, cylindric, 10 cm. long, 3 to 3.5 cm. in 

 diameter, densely covered with long white hairs; leaves minute, hidden under the wool, 7 mm. long; 

 spines solitary, white, 2 cm. long, slender; glochids white, bristle-like; flowers probably red; fruit 

 not known. 



Type locality: Mountains of Bolivia above Arequipa, Peru. 



Distribution: On the plains of the high Andes of Peru and Bolivia (altitude 4,000 

 meters) . 



This species is related to 0. floccosa, with which it often grows, but it takes on a very 

 different habit, growing in very dense, peculiar rounded mounds much higher than those 

 formed by 0. floccosa. 



Illustration: Engler and Drude, Veg. Erde 12: pi. 14. 



Figure 102 is from a photograph by H. L,. Tucker, near L,axsa, Peru, in 1911. 



Series 3. GLOMERATAE. 



Plants low, composed of globose or oblong joints, the spines, or some of them, modified into 

 flat papery processes. We recognize two species, confined to western Argentina. 



KEY TO SPECfES. 



Central spines papery; radial spines subulate 58. O. australis 



Spines, when present, all developed into long papery processes . . .59. O. glomerata 



