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 
(1.2m.). 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 3,8). Among the microphyllous trees the most 
abundant are Prosopis velutina, Acacia greggit, 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 (4m.), and by Opuntia 
fulgida and Opuntia mamillata (cholla), remarkable for the brilliance 
of their glistening straw-colored spines. Opuntia blakeana, Opuntia 
engelmanni, Opuntia toumeyt, and Opuntia discata are abundant repre- 
sentatives of the platopuntia group. The evergreen Covillea is greatly 
outnumbered by Fougquieria 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 californica (j ojobe) and the relatively large-leaved 
deciduous Jatropha cardiophylla are frequent, while a large number of 
less striking shrubs are common, including Franseria delioidea, Isocoma 
hartwegi, Encelia farinosa, Zizyphus lycioides var. canescens, Lycium 
torreyt, Momisia pallida, Krameria glandulosa, Trixis angustifolia var. 
latiuscula, Crassina pumila, and Psilostrophe coopert. 
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 
