Southeastern Washington and Adjacent Idaho. 53 
A comparison of a large number of temperature readings at 
one foot on the two slopes reveals the fact that at this depth the 
soils on the south slopes are from 3° to 5° F. warmer in early 
spring than those on the north slopes and that these differences 
may increase by late summer to 7°-10° F. In Table VIII the 
soil temperature from I to 5 feet on the two slopes at the base 
station is given. 
TABLE VIII 
Sort TEMPERATURE AT I-5 FEET oN Aprit 18 AND AUGUST I5, I9QI4, ON A 
NorTHEAST AND SOUTHWEST SLOPE, RESPECTIVELY 
April 18 August 15 
Depth ee nae See 
N.E. S.W, N.E. S.W. 
Ti, HOGES Opp CIE ea eae Ad. ORs 50.3 65.0 73.0 
BABU [one Shoxcine bis; Siel'el rs ns 45.1 50.0 61.7 70.0 
PRC Gaiaiete ite sha lets isle. aie! 45.0 48.2 58.0 66.2 
MRPR Cb hystes @ tiated ede © 45.0 47.0 57.2 64.4 
PRLCG Dees cro cievers's sterols, & ; 45.0 46.4 54.5 62.6 
The higher soil temperature prevailing on the south slopes 
has much to do with the earlier seasonal activities of many 
plants here than of those on north hillsides. 
Summarizing briefly the habitat conditions in the prairie, we 
find the north and northeast slopes less xerophytic than the south 
and southwest slopes. This is due in part to actually greater 
precipitation caused by blowing snow, and in part to soil texture, 
which is more open, has more humus, and a greater water hold- 
ing capacity. These factors are reflected in the greater amount 
of soil water and in lower temperatures. Likewise, these slopes 
are sheltered from the drying southwest winds, and from the 
perpendicular rays of the sun. This is reflected in slightly lower 
air temperature and greater humidity, and especially in the lower 
evaporating power of the air. 
These differences in habitat are reflected in the vegetational 
cover in a number of ways. The resumption of growth in late 
March or early April is often from 10 to 17 days earlier on the 
warmer exposed slopes. Likewise, the same species flower and 
dry up correspondingly earlier than on the sheltered slopes. The 
vegetational cover is less dense on the exposed slopes, often Io ta 
53 
