PHYTOGEOGRAPHY OF THE ARIZONA DESERT 187 



cardiophylla are common about the dykes and rocky places. In 

 such habitats are also found Eriogonum wrightii, Coleosanthus 

 coulteri, Tragia and Krameria. Most conspicuous of all, because 

 dark evergreen, is a dotting of Yucca brevifolia. Two platopuntias, 

 Opuntia discata and 0. chlorotica, and a species of cylindropun- 

 tia are found. A short-spined relative of Echinocereus fendleri 

 inhabits the dykes, in which habitat is also found, as is usually 

 the case, the rainbow cactus, Echinocereus dasyacanthus. Even 

 the sunset cactus, Mamillaria grahami, is still present, and becomes 

 decidedly abundant on the desert hills below. Three species of 

 Echinocactus are found growing in close proximity, one of these 

 being E. emoryi, a species of striking beauty which is also found 

 occasionally at lower elevations. Calliandra eriophylla now be- 

 comes an abundant dwarf shrub on rocky areas of sunny slopes 

 just as at the same altitudes elsewhere. From this characteriza- 

 tion of the physiognomy and partial census of the species we may 

 know that we have here an elevation of 4000 to 4500 feet. 



The steeper slopes, especially on north aspects, are taken by an 

 often dense growth of Simmondsia calif ornica, just as they would 

 be taken by evergreen oaks if the mountains were higher. This 

 dioecious evergreen shrub with dark and coriaceous foliage and 

 somewhat acorn-like fruit, takes the place of the chaparral oaks 

 in exactty similar though lower habitats and justifies the local 

 name "desert oak" in more ways than one. The fruit of the 

 jojobe, which is the Mexican name for this shrub, and that of 

 the sahuaro form two staples articles of food for the numerous 

 Papago Indians inhabiting this region. The desert oak is the 

 most abundant evergreen shrub of the strictly woody class that 

 is found in the desert mountains. 



The summits of the middle Quijotoa mour.tair s present a differ- 

 ent appearance from the Comobabi range. The geologic formation 

 is an old one, and the rock a granite, giving rise to the Quijotoa gold 

 placers at the eastern base of the mountains. The range is narrow 

 and the peaks are sharp, probably not exceeding 4500 feet in 

 elevation. To the north the crest of the range is similar, but less 

 in altitude, being flanked on the west by the Sierra Blanca. The 

 southern part of the range, in which its axis extends due north and 



THE PLANT WORLD, VOL. 15, NO. 8, AUGUST, 1912 



