CACTACE^ 



689 



tomentum and short slender pale bristles, each areola bearing at first 5-15 stout 

 stellate-spreading light yellow spines of nearly equal length, f -1' long and inclosed 

 in loose lustrous sheaths, additional spines developing in succeeding years at the upper 

 margins of the areolae, the tubercles of old branches being sometimes furnished with 

 from 40-60 spines persistent on the branches for 4-6 years. Bark of the trunk and 

 of the large limbs about ^' thick, separating freely on the surface into large thin 

 loosely attached scales varying in color from brown to nearly black on the largest 

 stems, and unarmed, the spines mostly falling with the outer layers from branches 

 3'-4' thick. Wood of old trunks light, hard, pale yellow, with broad conspicuous 

 medullary rays, well marked layers of annual growth, and a thick pith. 



Distribution. Plains of Arizona south of the Colorado plateau, and in the adja- 

 cent region of Sonora; not rare; apparently most abundant and of its largest size on 

 the mesas near Tucson, at elevations between 2000 and 3000 above the sea. 



2. Opuntia spinosior. Tourney. Tassajo. 



Leaves terete, tapering gradually to the setulose apex, about 1' long, remaining 

 on the branches four to six weeks. Flowers opening in April and May and remain- 

 ing open for two or three days, 2'-2i' in diameter, with ovaries about 1' long, obovate 

 sepals, broadly obovate dark purple petals, sensitive red stamens, and a 6-9-parted 

 stigma. Fruits clustered at the ends of the branches of the previous year, persistent 

 on the branches during the winter and occasionally during the following summer 

 and then sometimes proliferous, oval or rarely globose or hemispherical, frequently 

 2' long and 1|' thick, with yellow acrid flesh and 20-30 tubercles very prominent 

 during the summer, nearly disappearing as the fruit ripens and enlarges, leaving 



^6o 



J 



it marked only by the small oval areolae covered with short bristlfes, and bearing 

 numerous slender spines deciduous in December as the fruit begins to turn yellow; 

 seeds nearly orbicular, slightly or not at all beaked, ^'-\' in diameter, and marked 

 by linear conspicuous commissures. 



A tree, with an erect trunk occasionally 10 high and 5'-10' in diameter, numerous 

 stout spreading limbs forming an open irregular head, and branches with joints 4'- 

 12' long, ^'-V thick, covered with a thick- epidermis varying from green to purple 

 and usually developing woody skeletons during their second season, their tubercles 

 prominent, compressed, ovate, ^'^' long. Areolae oval, clothed with pale tomentum 



