368 BOTANICAL GAZETTE [NOVEMBER 
bunch-grasses, and others. A few species commonly found in the undergrowth 
of unmixed but not densely shaded forest are Harbouria trachypleura, Aletes 
acaulis, Senecio (one or two spp.), Solidago (several spp.), and Pentstemon 
humilis. . 
PINYON-CEDAR ASSOCIATION 
CLEMENTS (1, p. 8), foothill woodland formation; SHANTZ (22, p. 184); 
WATSON (25, pp. 205-207), cedar and pinyon formations. 
The pinyon, or nut pine, Pinus edulis, and less abundantly the 
cedar of the southern Rockies, Juniperus monosperma, are conspicu- 
ous plants in the mountain-front of the southern part of the state 
and in the adjoining foothills. Toward the south conditions are 
generally more xerophytic at the mountain-front; there the rock 
pines are common only in higher elevations; they are replaced below 
by the pinyon. Like the rock pines farther north, the pinyons show 
local extension eastward into the plains, in rocky habitats, such as 
the canyon-walls of mck outcrops, and the bluff-crests of the plains 
stream valleys. 
Between the trees are plains or semi-desert plants, many southerly species 
being present which are rare or absent farther north than about Colorado 
Springs. One of the most notable of these is the candlestick cactus, Opuntia 
arborescens, common at the mountain-front on rock-strewn slopes and mesas. 
The pinyons (and to a smaller extent the cedars) are typically broadly 
rounded, the diameter of the crown being usually as great as the height of the 
tree, which is rarely more than 12-15 ft. The trees are usually separated so 
that the crowns are distant from each other by a diameter or a little less, in the 
closer stands. The writer has never seen a really closed pinyon forest in which 
the crowns would form a continuous canopy. The interval between trees 
rically developed. Where the habitat is extensive, the pinyons are quite 
uniformly dotted over the general area. On rocky ridges and mesa-crests the 
trees are in ragged lines, in small clumps, or irregularly scattered. 
QUERCUS ASSOCIATION — 
LEMENTS (1, p. 6) and SHANTz (22, p. 179), foothill thicket formation, in 
part; WATSON (25, pp. 207-210), white oaks in the yellow pine association. 
East of the range-crest oaks may be seen nearly as far north as 
Denver; however, they form more extensive growths to the south- 
ward. North of the Platte-Arkansas divide they are perhaps more 
abundant at the mountain-front and in the Plum and Cherry Creek 
