50 A Study of the Vegetation of 
at depths of 4 and 5 feet after April 18, but from June 3 to 
August 15 the soil moisture was gradually depleted at all depths 
to 5 feet. The heavy horizontal bars give the wilting coefficients 
at the depths indicated. On July 6 no water was available in the 
second foot of soil and only a small margin over the wilting co- 
efficient was present at 3 feet. The broken line indicates that on 
December 13 of the preceding winter the soil was drier at three, 
four, and five feet respectively, than at any other time indicated. 
The fall rains had not then penetrated beyond 2 feet. While ex- 
cavating root-systems during the fall, winter, and spring, an ex- 
cellent opportunity was offered to study the rates of penetration. 
The water penetrated very slowly and at about equal rates on all 
slopes. By October 18 only the surface layer of 8 inches was 
wetted, and in late March the wet soil reached a depth of not more 
than 4 feet. The dotted graphs in the figure indicate the soil 
moisture on the northeast slope. 
Aside from the lower temperature and greater humidity of the 
north slopes, the actual amount of moisture available to these 
soils is important in explaining the observed differences in mois- 
ture content. The wind 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 to 8 inches deep, while on the sheltered 
slopes at the same time drifts 48 to 52 inches were measured. 
The second, while an extreme case, is illustrative. During Feb- 
ruary and March, 1913, while only one foot of snow lay on the 
south and southwest slopes, the protected northeast slopes were 
covered with drifts of well-packed snow from Io to 13 feet deep. 
In Fig. 14 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 3-5 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 condi- 
tions similar to those explained for the corresponding graph in 
Fig. 14. On August 15 no soil water was available above the 
two-foot level. If the graphs in this figure are compared with 
the corresponding graphs in the preceding one it may be readily 
50 
