Southeastern Washington and Adjacent Idaho. 47 
than on the exposed slopes, as was shown by six sets of humus 
determinations made for each foot of soil on the two slopes, re- 
spectively. This combination of more clay and more humus on 
the north and northeast slopes reflects itself especially in the 
increased water holding capacity of the soil. An average of six 
determinations gave a mean water holding capacity of 56 per 
cent. (based on dry weight at 104° C.) for the first foot of soil 
on north slopes, as compared with 48 per cent. on south slopes. 
This margin of 8 per cent. is rather an important difference in 
favor of the soils on the protected slopes, since the wilting coeffi- 
cients of the two soils differ but little. These substratum differ- 
MAY JUNE JULY AuGcusT SEPT. 
[5 ea a | 
Be ey Soe 
dice 
JSaSeee 
“til 
i. = ill TI 
| BS | il 
Bt | to 
ee 
Fic. 12. Graphs showing the march of soil water to a ‘pRis of 10 
inches from April to September, 1913 (heavy lines), and from May to 
August, 1914, on a northeast slope (solid lines), and a southwest slope, 
respectively. AT 
