DIFFERENT ALTITUDES IN COLORADO 41 
are much the same. Thus, in the montane area, practically all 
the species present in the early stages persist throughout; the 
relative proportions change, however, and more species enter the 
association as the soil becomes finer grained and as humus accu- 
mulates. 
Occurrence of these grasslands is wide spread. In the lower 
part of the foothill region typical vegetation is a coniferous 
savanna. In the interspaces between trees there is dry grassland. 
Many intervales, locally known as ‘‘parks,’’ are almost entirely 
without trees. In both foothill and montane areas many stream 
terraces, alluvial fans, and south-facing hill slopes support dry 
grassland. In the subalpine zone conditions for forest develop- 
ment are more favorable, and grassland is likely to be confined 
to burned areas or to wind-swept south exposures. 
ENVIRONMENTAL INFLUENCES 
The stations where most of the collections were made, with 
their altitudes, are as follows: 
Boulder, 5,340 ft.; mountain front, mesa area. 
Crescent, 7,457 ft.; lower foothills. 
Rollinsville, 8,367 ft.; upper foothills. 
Sulphide, 8,508 ft.; upper foothills. 
Smartweed Lake, 8,420 ft.; upper foothills. 
Tolland, 8,889 ft.; montane. 
Bryan Mountain, 11,000 ft.; subalpine. 
Boulder, Crescent, Sulphide and Bryan Mountain are in Boul- 
der County; Rollinsville, Smartweed Lake and Tolland are in Gil- 
pin County (see Fic. 2). Many other stations through both of 
these counties have been visited. 
The soil of all the dry grasslands is disintegrated rock, rather 
coarse grained, often with pebbles and boulders. It readily 
permits penetration of rain water but it dries quickly. As shown 
in a previous paper (10) the water content is low, averaging about 
7 per cent, but the wilting coefficient is correspondingly low, 
about 5; figures being for 3 dm. depth. The soils warm up quickly 
through direct insolation and show a higher temperature than the 
air. Floristic differences in the dry grasslands do not depend on 
soil quality for this is much the same in all, but rather on air 
temperature (TABLE I), soil temperature (TaBLE II), and pre- 
