CACTACE^E 761 



A tree, with a more or less flexuous trunk occasionally 12 in height and sometimes a foot 

 in diameter, a symmetric head of stout wide-spreading branches and thick pendulous joints 

 sometimes almost hidden by the long conspicuous spines and beginning to develop their 

 woody skeletons during their second or occasionally during their third season, the terminal 

 or ultimate joints ovoid or ovoid-cylindric, tumid, crowded at the end of the limbs, pale 

 olive color, 3'-8' long, often 2' in diameter, with broad ovoid-oblong tubercles, f'-f in 

 length. Areolae of pale straw-colored 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 margin of the areolae, the tubercles of old branches being sometimes fur- 

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

 and of the large limbs about J' 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 un- 

 armed, 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 adjacent 

 region of Sonora; not rare; apparently most abundant and of its largest size in the United 

 States on the mesas near Tucson, Pima County, at altitudes between 2000 and 3000. 



2. Opuntia spinosior Tourney. Tassajo. 



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

 branches from four to six weeks. Flowers opening in April and May and remaining open 



Fig. 684 



> 



for two or three days, 2'-2' in. diameter, with ovaries about 1' long, obovate sepals, broad- 

 obovate dark purple petals, sensitive red stamens, and a 6-9-parted stigma. Fruits 

 clustered at the end of the branches of the previous year, persistent during the winter and 

 occasionally during the following summer and then sometimes proliferous, oval or rarely 

 globose or hemispheric, frequently 2' long and If thick, with yellow acrid flesh and 20-30 

 tubercles very prominent during the summer, nearly disappearing as the fruit ripens and 

 enlarges, leaving it marked only by the small oval areolae covered with short bristles, 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 and^ 



