GURRENT LIEERATURE 
NOTES.F.OR STUDENTS 
Ecology of the Santa Catalina Mountains.—The Santa Catalina Moun- 
tains of southeastern Arizona afford unusual opportunities for ecological studies 
by displaying a rich vegetation in the midst of a semi-arid region. They rise 
from a basal elevation of 3000 feet to a height of 9150 feet, and their proximity 
to Tucson has lead to their study by members of the staff of the Desert Labora- 
tory and of the University of Arizona. As a result of such an investigation, 
SHREVE’ has made an analysis of the vegetation in relation to climatic factors. 
In general these mountains are characterized by rugged ridges of gneissic rock, 
and steep, rather narrow, drainage canyons without mountain parks or 
meadows. Only above 7500 feet is there any modification of the soil due to 
the accumulation of humus, while below that altitude the pockets and crevices 
are filled with a loam soil mixed and often with its surface covered with coarse 
angular fragments. About the base of the mountain are alluvial slopes of 
straight profile accumulated by violent and intermittent stream flow, and 
designated by their popular Spanish name “‘bajada.”’ In this study the vegeta- 
tion of the upper bajadas is included, giving a picture of the plant life by which 
the higher elevations are surrounded and from which they derive many of 
their characteristic species. 
Three vegetational regions are distinguished: the desert, with an alti- 
tudinal range from 3000 feet on the upper bajadas to 4000-4500 feet upon the 
mountain slopes; the scrub or semi-desert, here designated “‘encinal,” with an 
upward limit of 6000-7000 feet; and forest reaching to and most highly devel- 
oped upon the mountain tops. The desert vegetation of the upper bajadas 
and mountain slopes differs from that of the lower plains principally in the 
greater number both of species and of individuals there present, but agrees 
in general openness of stand, lowness of stature, and diversity of types, com- 
prising principally such forms as stem succulents, microphyllous and sclero- 
phyllous shrubs, macrophyllous deciduous shrubs, perennial grasses, root 
perennials, and ephemeral herbaceous plants. Conspicuous examples of such 
types-are seen in Cereus giganteus, Echinocactus spp., Opuntia spp., Ske te 
velutina, Acacia Greggii, Parkinsonia microphylla, Covillea tridentata 
splendens, Jatropha cardiophylla, and Franseria deltoidea; while at ake cpa 
* SHREVE, Forrest, The vegetation of a desert mountain range as conditioned 
by climatic factors. Carnegie Inst. Wash. Publ. no. 217. pp. 112. pls. 36. figs. 17- 
IgI5. 
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