194 



THE CACTACEAE. 



horses. The wide distribution of the species is doubtless largely due to the fact that the 

 joints are so easily scattered. A hybrid with 0. tortispina has been found in Kansas 

 (Rose, No. 17132). 



The plant is of especial interest as the most northern in distribution of the opuntias. 



It is stated that Opuntia ccrvicornis Spath (Cat. 156. 1906-7) is "probably a hybrid 

 of which 0. fragilis is a parent" (Kew Bull. Misc. Inf. 1907: App. 74. 1907). 0. sabinii 

 (Pfeiffer, Enum. Cact. 147. 1837) was given as a synonym of 0. fragilis. 



Illustrations: Cact. Journ. i: too; Diet. Card. Nicholson 2: f. 752; Forster, Handb. 

 Cact. ed. 2. f. 132; Gartenflora 30: 413; Pac. R. Rep. 4: pi. 12, f. 9; Riimpler, Sukkulenten 

 f. 126; W. Watson, Cact. Cult. f. 78; Wiener Illustr. Gartenz. io:f. 113, all as Opuntia 

 brachyarthra. Illustr. Fl. 2 : f . 2532 ; ed. 2. 2 : f . 2991 ; Pac. R. Rep. 4 : pi. 24, f . 5. 



Plate xxxv, figure i, shows old and young joints of the plant collected by C. Birdseye 

 at Florence, Montana, in 1910. Figure 239 is from a photograph of the plant taken by 

 E. R. Warren at San Acacio, Colorado, in 1912. 



FIG. 239. Opuntia fragilis. 



217. Opuntia arenaria Engelmann, Proc. Amer. Acad. 3: 301. 1856. 



Roots in clusters of 10 to 15, spindle-form, somewhat fleshy; stem prostrate, 2 to 3 dm. long, 

 much branched; joints during growing season quite turgid, afterwards much thinner, 4 to 8 cm. 

 long, half as broad as long; areoles large, numerous, filled with brown wool, glochids, and spines; 

 spines 5 to 8 from an areole, 2 or 3 much longer than the others, sometimes 4 cm. long; flowers red, 

 7 cm. broad; fruit dry, spiny, 3 cm. long; seeds large, 7 cm. broad. 



Type locality: Sandy bottoms of the Rio Grande near El Paso. 



Distribution: Texas and southern New Mexico. 



This species is very rare and has been reported only a few times. Dr. Rose, who has 

 repeatedly collected at El Paso, was never able to find it until October 1913, and then but 

 a single plant about 8 miles above El Paso on the New Mexican side of the Rio Grande. It 

 grows in nearly pure sand not far above the level of the river. 



