VEGETATION OF THE SANTA CATALINA MOUNTAINS. 17 



deserts, the last is at least characteristic of the less pronounced deserts 

 of the southwestern United States and of Mexico. The openness of the 

 stand is such that it is possible in all places to ride a horse through the 

 vegetation and to take whatever course the rider may wish, with only- 

 occasional digressions of a few yards from the general direction of 

 travel. The stature of the vegetation is such that it would be possible 

 for the rider to keep almost constantly in view another mounted man 

 half a mile distant. The columnar giant cacti reach a maximum height 

 of 40 feet (12 m.) and the trees a height of 20 to 25 feet (6 to 8 m.). 

 The great bulk of the shrubs and succulents, however, are not more 

 than 6 feet (2 m.) in height, and many of them are less than 4 feet 

 (1.2 m.) . Among the commonest vegetation types are stem-succulents, 

 microphyllous and sclerophyllous trees and shrubs, macrophyllous decid- 

 uous shrubs, perennial grasses, and root-perennial and ephemeral her- 

 baceous plants. 



Largest and most conspicuous of the succulents is Carnegiea gigantea 

 (saughuaro, giant cactus), which is here in its optimum habitat and 

 very abundant (plate 3, b) . Among the microphyllous trees the most 

 abundant are Prosopis velutina, Acacia greggii, Acacia paucispina, and 

 the green-barked Parkinsonia microphylla (palo verde). The much- 

 branched arborescent types of cacti are represented by Opuntia versi- 

 color, which attains a maximum height of 12 feet (4 m.), and by Opuntia 

 fulgida and Opuntia mamillata (cholla), remarkable for the brilliance 

 of their glistening straw-colored spines. Opuntia blakeana, Opuntia 

 engelma7ini, Opuntia toumeyi, and Opuntia discata are abundant repre- 

 sentatives of the platopuntia group. The evergreen Covillea is greatly 

 outnumbered by Fouquieria splendens (ocotillo). The globular Echino- 

 cactus wislizeni (bisnaga) attains a height of 4 feet (1.3 m.) with an 

 even greater girth. Similar in form but never exceeding a foot in 

 height are Echinocereus fendleri and Mamillaria grahami. The sclero- 

 phyllous Simmondsia calif arnica (jojobe) and the relatively large-leaved 

 deciduous Jatropha cardiophylla are frequent, while a large number of 

 less striking shrubs are common, including Franseria deltoidea, Isocoma 

 hartwegi, Encelia farinosa, Zizyphus lycioides var. canescens, Lycium 

 torreyi, Momisia pallida, Krameria glandulosa, Trixis angustifolia var. 

 latiuscula, Crassina pumila, and Psilostrophe cooperi. 



The seasonal rains of winter and those of summer cause activity of 

 foliation and growth on the part of all of the smaller shrubs. The 

 winter rains cause foliation in Parkinsonia and Fouquieria, but not in 

 Prosopis and the species of Acacia. Neither do they initiate growth 

 in Parkinsonia, Fouquieria, nor any of the cacti. The two widely 

 separated seasons of rain bring forth two wholly distinct sets of herba- 

 ceous ephemeral plants, at the same time that each season causes activ- 

 ity upon the part of some of the root-perennials. The ephemeral plants 

 may form a dense carpet over both the Upper Bajadas and the Lower 



