5O 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 w r ater 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 10 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 35 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 



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