408 BOTANICAL GAZETTE [yuNE 
During a portion of the growing seasons of 1909 and 1913, 
thermographs were run by members of the staff of the Mountain 
Laboratory. They show that the daily range of temperature may 
run high. This is particularly the case during clear weather. The 
daily minimum temperature is usually reached between 5:00 and 
6:00 A.M., the daily maximum between 1:00 and 2:00P.M. In 
1909 the latest freezing temperature was June 22; in 1913 the 
temperature sometimes went down to freezing or below throughout 
July, and on August 1 of that year the minimum was 32° F._ After- 
noon showers of short duration during June, July, and August are 
common. Prolonged rains are infrequent. Although there is - 
considerable snow, its accumulation on the high terraces, particu- 
larly, is largely prevented by their exposure to the sweep of winds 
from the west. There are large drifts of snow, however, in pro- 
tected situations. 
RAMALEY and MITCHELL (18) in 1909 determined the relative 
humidity at a number of Park stations. It varied on July 8 from 
39 per cent on the north exposure of a railroad cut to 65 per cent 
in the lodgepole pine forest; on July 12, from 39 per cent in the 
railroad cut to 71 per cent in the forest. 
Successions 
FLOOD PLAIN SUCCESSION 
Boulder Creek is a meandering stream with considerable cutting 
power. Along its course in the Park one may find shores of erosion, 
of deposition, and numerous oxbows in all physiographic and vegeta- 
tive stages, and also well defined stream terraces. Hence there is 
an unexcelled opportunity here, as may be judged somewhat from 
a reference to fig. 1, to study succession on a mountain flood plain. 
Two types of embryumic flood plains occur along Boulder Creek 
in its course through the Park: (1) those composed of well rounded 
boulders (cobblestones), averaging 2—6 inches in diameter, with a 
slight admixture of coarse gravel (fig. 4); and (2) those made of 
sand and silt (fig. 5). The former are initially xerophytic, the 
latter hydrophytic. 
Shores of the cobblestone type may be partly under water during 
the spring or in wet seasons, but are usually bare in summer and 
