138 



THE CACTACEAE. 



In 1885 C. G. Pringle again collected this species near Chihuahua City and it was dis- 

 tributed as 0. filipendula, and there Coulter leaves Pringle's specimen (Cont. Nat. Herb. 

 3: 428). Dr. E. Palmer collected an abundance of material in 1908 which enabled us to 

 reestablish 0. pottsii, which Coulter omits and Schumann lists under unknown species. 



If these Chihuahua specimens are the same as the Texas plants, as Coulter beUeved 

 and as we regard them, then Opuntia filipendula must give place to the older name of Salm- 

 Dyck. 



Illustrations: Cact. Mex. Bound, pi. 68; Forster, Handb. Cact. ed. 2. f. 10, 131; Suppl. 

 Diet. Gard. Nicholson 2: f. 605; W. Watson, Cact. Cult. f. 81, aU as Opuntia filipendula. 



Figure 173 shows a joint of a plant collected by Dr. Rose in the valley of the Rio 

 Grande below El Paso, Texas, in 1913. 



135. Opuntia setispina Engelmann in Salm-Dyck, Cact. Hort. Dyck. 1849. 239. 1850. 



Stem branching and spreading, sometimes 9 to 12 dm. broad, with some of the branches com- 

 posed of 3 or 4 joints, erect and 6 dm. high; joints deep bluish green, somewhat glaucous, often 

 purpUsh at the areoles, sometimes more or less tinged with purple throughout, obovate to orbicular, 

 5 to 15 cm. in diameter; leaves minute, subulate; spines i to 6 from an areole, white, 2 to 3 cm. 

 long; glochids yellow, very conspicuous on old joints; flowers yellow; fruit purplish, about 4 cm. long. 



Fig. 173. — Opuntia pottsii. X0.4. 



Fig. 1 74. — Opuntia setispina. X0.4. 



Type locality: Pine woods in the mountains west of Chihuahua, Mexico (fide Engel- 

 mann, Proc. Amer. Acad. 3: 294. 1856). 



Distribution: Western Chihuahua, Mexico. 



This species has long been known only from the type specimens; but in 1908 Dr. Rose 

 visited western Chihuahua, where this species is quite common; our description is based 

 largely upon the specimens he then collected. 



Figure 174 represents a joint of the plant collected by Dr. Rose near Mifiaca, Chi- 

 huahua, in 1908. 



136. Opuntia mackensenii Rose, Contr. U. S. Nat. Herb. 13: 310. 191 1. 



Plants low, with thick, tuberous roots, spreading, usuaUy resting on the edges of the joints, but 

 some of the branches often erect; joints orbicular to obovate, 10 to 20 cm. long, rarely broader than 

 long, pale and glaucous when young, deep green when older; areoles small, the lower ones without 

 spines, the upper ones with i to 4 spines; spines white or brown, or brown at base and white above, 

 somewhat flattened and twisted, slender, 5 cm. long or less; glochids brown; flowers of medium size, 

 7 to 8 cm. broad, yellow with a reddish brown center; stigma-lobes 7 to 9, white; fruit spineless, 4 to 

 6 cm. long, truncate or nearly so at apex, rose-purple; seeds suborbicular, 5 to 6 mm. broad, acute 

 on the margin. 



