Southeastern Washington and Adjacent Idaho. 49 
It is apparent from these data that prairie plants must obtain 
their water from greater depths than ten inches, at least during 
the dry summers. In fact, some of these plants penetrate to a 
depth of 12 or 13 feet, while most of them get the bulk of their 
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HL 
NI 
in 
f 
NE 
MK 
NHR 
34 
3 April 18 
Fic. 13. Graphs showing the march of soil water to a depth of 5 teet 
on a southwest slope from April 18 to August 15, 1914; and the water con- 
tent of the soil on December 13, 1913. The dotted lines indicate water 
contents on a northeast slope. 
water from the second to the sixth foot of soil (Figs. 15a, 150, 
and 15¢). Consequently, a consideration of soil moisture at these 
depths is imperative for a proper understanding of root environ- 
ment. These deeper soil water determinations (many to a depth 
of 8 feet) were taken at intervals from December, 1912, to 
August, 1914. Fig. 13 (solid lines) shows the march of soil water 
from early spring until late summer of 1914, on a southwest slope. 
It is apparent that there was still a downward movement of water 
49 
