418 
ranging from the Upper Pecos in New Mexico to southern California, 
and extending southward into Chihuahua; and polyacanthus, most 
abundant of all the group, extending from El] Paso to southern Cali- 
fornia and southward into the mountains of Chihuahua on the east 
and Lower California on the west. 
Taking our species of Cereus as as a whole, therefore, they may be 
broadly thrown into two geographical groups, the El Paso forms and 
the Arizona forms, the former, containing about two-thirds of the spe- 
cies, and of Chihuahua origin, the latter of Sonoran origin. 
6. OPUNTIA Mill. Gard. Dict. ed. 7 (1759). 
Plants with flat or cylindrical more or less tuberculate joints: leaves 
conspicuous but caducous, each with an axillary “ pulvinus” which is 
usually clothed with soft wool intermixed with barbed bristles at the 
upper edge and usually bearing spines at the lower edge: flowers 
developed from the bristle-bearing part of the pulvinus, with rotate 
corollas: ovary covered with the caducous leaves bearing axillary wool 
and often bristles and spines: fruit dry or succulent: seeds large, 
usually flattened and discoid, often margined: cotyledons foliaceous, 
curved about the endosperm. Consolea Lem, (1862) ; Tephrocactus Lem, 
(1868); Micindica St. Lag. (1880). 
The most difficult of our genera on account of its exceedingly ill-defined specific 
lines. Little more is attempted in the following pages than a tentative presentation 
of our material, and little more can be done until numerous forms have been studied 
under cultivation. 
I, PLATOPUNTIA. Joints flat, moreor lessround: spines never sheathed : 
seeds with prominent margin. 
*“ Petals small, subulate, suberect: stigmas 1 to 3, acute. 
1. Opuntia stenopetala Engelm. Syn. Cact. 289 (1856), 
Prostrate, with large thick joints 15 to 20 em. broad: pulvini 3 to 3.5 
em. apart on surtace of joint, but very crowded at margin, with much 
dirty- white wool and short dark-brown bristles: spines 1 to 3 (often with 
1 to 3 smaller ones added), 3.5 to 5 em. long, curved deflexed or spread- 
ing, compressed, reddish-black with lighter tip: flowers orange, its 
pulvini very woolly: sepals and petals numerous, linear-subulate and 
suberect: style undivided at apex: ovary 18 mm. long: fruit unknown. 
(1. Cact. Mex. Bound. t. 66)—Type, Gregg 295 in Herb. Mo. Bot. 
Gard. 
“Battlefield of Buena Vista, south of Saltillo” (Gregg). 
Specimens examined: COAHUILA (Gregg 295 of 1848: Weber of 1865- 
1866), 
The Mexican O. grandis has similar flowers, but is an erect plant, with few white 
spines and two or three acute stigmas. 
