PRAIRIE PLANTS OF SOUTHEASTERN WASHINGTON 



235 



temperatures and greater humidity of the north slopes, the actual 

 amount of moisture available to these soils is important in ex- 

 plaining the observed differences in moisture content. The same 

 agency that has so profoundly affected the topography, namely 

 the wind, also drifts over to the sheltered slopes much snow, 

 which upon melting adds to the soil water. Two examples will 

 suffice. In February 1914, exposed prairie slopes had a blanket 

 of snow from 5-8 inches deep, while on the sheltered slopes at the 

 same time drifts 48-52 inches in depth were measured. The 

 second, while an extreme case, is illustrative. During February 



TABLE 3 

 The march of soil water on a northwest and south slope respectively. 1914 



and March, 1913, while only 1 foot of snow lay on the south 

 and southwest slopes, the protected northeast slopes were covered 

 with drifts of well packed snow from 10-13 feet deep. 



In figure 3 is shown the march of soil water similar to that in 

 the preceding figure, but for soils of a northeast slope. Here 

 again, the downward movement of water at 3 to 5 feet after 

 April 18 is apparent, as is also the gradual depletion of soil water 

 at all depths to 5 feet. Likewise, the broken graph indicates 

 conditions similar to those explained for the corresponding graph 

 in figure 2. On August 15, no soil water was available above 

 the 2-foot level. If the graphs in this figure are compared with 

 the corresponding graphs in the preceding, it may be readily 



