136 
long: pulvilli crowded, bearing very numerous slender reddish bristles and no spines: 
flowers yellow, 6.5 cm. in diameter, with an obovate ovary covered with numerous 
pulvilli.—Common along the Rio Grande near Presidio del Norte. 
**NEH* Diffuse: joints swollen: spines very numerous: fruit dry and spiny. 
12. O. arenaria Eng. Ascending, spreading 6 to 9 dm., 15 to 30 em. high: roots 
stout, creeping horizontally : joints obovate, teretish or somewhat compressed, tuber- 
culate, 3.5 to 7.5 em. long, 2.5 to5cm. wide: pulvilli somewhat crowded, very bristly 
with pale bristles; 1 to 4 stouter spines white or grayish-brown (18 to 30 mm. long), 
with 2 to 6 white and shorter lower ones: flowers sulphur-yellow, 5 to 6.5 cm, in di- 
ameter,with emarginate petals and an obovate ovary: fruit oblong, spinose, about 
2.5 em. long, with a funnelform umbilicus.—Sandy bottoms of the Rio Grande near 
El Paso. 
§ 2. Joins cylindrical, more or less tuberculated: fruit dry or but little fleshy: seed not 
margined, or scarcely so. 
* Low plants, with clavate joints, without a firm woody skeleton: flowers yellow : fruit dry 
and very bristly. 
13. O. Emoryi Eng. Joints long (12.5 to 22.5 em. long and 2.5 to 3.5 em. thick), 
clavate-cylindrical, with linear-oblong and very prominent tubercles (2.5 to 3.5 em. 
long): spines numerous (15 to 30) in the upper bundles, the 5 to 9 inner ones stouter, 
angular-compressed, the longest 3.5 to 6.5 cm. long: flowers yellow, reddish without: 
fruit 5 to 6.5 em. long.—Dry soil, about E] Paso, which seems to be its eastern limit. 
14. O. Schottii Eng. Joints 5 cm. long, with elongated tubercles 16 to 18 mm. 
long: pulvilli with few bristles; spines less numerous (10 to 14), usually 4 inner ones 
stouter and broader (3.5 to 5 cm. long), the upper one being triangular in section, the 
others plano-convex, the 8 to 10 outer ones more slender and radiate (8 to 18 mm. 
long), all dirty-red and very rough: fruit ovate.—Dry hills near the mouths of the 
San Pedro and Pecos. ‘Distinguished by the broad and very rough dirty-red spines 
(larger ones with a white margin) and by the smaller number of bristles on the pul- 
villi of both joints and fruit” (Hngelmann), 
15. O. Grahami Eng. Roots fusiform: joints 3.5 to 5 cm. long, with oblong tu- 
bercles 12 to 14 mm. long, and ovate-cuspidate leaves rarely 4 mm. long: spines 8 to 
13, slender and reddish, the inner 4 to7 teretish or angled, the outer 4 to 6 short,— 
Sandy bottoms of the Rio Grande, from E] Paso downwards, but probably not below 
the ‘‘Great Bend.” 
* * More or less erect and much-branched plants, with cylindric joints having a solid or 
tubular and reticulated woody skeleton, 
+ Spines more or less numerous: joints prominently tuberculate. 
16. O. Davisii Eng. Spreading and somewhat procumbent, about 45 cm. high, 
divaricately much branched, with dense wood: younger joints erect, elongated, at- 
tenuate at base, rather slender, 10 to 15 cm. long, with oblong-linear tubercles 14 to 
16 mm. long: spines 9 to 13, the interior 4 to 7 subtriangular, reddish and coated with 
a loose straw-colored sheath, 2.5 to 3.5 cm. long, the lower 5 or 6 slender (6 to 12 mm, 
long): flowers yellow: fruit ovate, dry and spiny, 2.5 em. or more long.—On the 
Llano Estacado. 
17. O. arborescens Eng. Tree-like, 15 to 18 dm. (further south 30 to 60 din.) high, 
with verticillate horizontal or pendulous branches and reticulate-tubular wood: 
joints verticillate, cylindrical, with prominent crested tubercles: spines 8 to 30, 
stellate-divaricate: flowers large, purple: fruit nearly hemispherical, tuberculate- 
cristate, yellow, unarmed, and almost dry.—Prairies and highlands of western Texas. 
The so-called ‘‘skeleton” (wood) of this handsome purple-flowered species forms a 
‘theavy, hollow cylinder, with rhombic holes or meshes corresponding to the tubercles 
and spine-bunches of the plant” (Rothrock). 
