354 BOTANICAL GAZETTE [NOVEMBER 
It is perhaps the conspicuousness of the trees, especially in distant 
views and in profiles of slopes (fig. 8), which gives the common but 
not wholly true impression that the foothills are generally forested 
with conifers. The rock pine, the most generally distributed conifer 
of the region, forms relatively few and scattered true forests; it 
usually grows in very open formation, in mixture with the grassland 
which covers most of the surface. The general aspect of the vege- 
tation is that of an open growth of grassland and scattered pines 
over a dry and partly bare upland of granitic hills. Semi-meso- 
phytic and phytic communities, of both herbaceous and woody 
plants, occur; but only locally, in moister or more sheltered ravines 
and canyon-bottoms. The vegetation complex of the mountain- 
front is a modification of that of the foothills, but is less simple in’ 
composition. 
Environmental conditions 
The Front Range in Colorado is an up-arched and dissected 
plateau of crystalline rocks, the tops of most of the hills forming the 
remains of a peneplaned surface; scattered higher mountains 
represent monadnocks surmounting the former general level. The 
eastern part of the plateau slopes gently toward the plains, the 
sedimentary strata of which are here upturned against the granitic 
rocks, forming sloping crags on the outer face of the foothills, or 
hogback ridges separated from the hills by north-south valleys. 
The physical geography of the Front Range is described by DAvIS 
(5). Itis with the lower, more easterly part of the granitic plateau 
and with the more irregular country of the mountain-front that 
this study has to do. 
The climate of the foothill region is dry, though not enough so 
to be called semi-arid, like that of the plains. Rainfall at the 
mountain-front is from about 15 to 18 inches average for the year; 
higher in the northern part of the state and onthe elevated Platte- 
Arkansas divide, lower south of the Arkansas River. The upper 
foothills receive about 18-20 inches. Annual variation of rainfall 
is considerable. Most of the rain comes during the growing season. 
At Boulder, and in the northern foothills generally, April and May 
are the rainiest months; in the southern foothills the earlier part 
of the summer is drier than later. This, with higher summer 
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