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 



4' 



flugust 15 

 8 July 6- 

 fluqust 15 

 Jun< 



jne3 



Dec. 13 1913 



flpril 16 



flpri||8 



FIG. 13. Graphs showing the march of soil water to a depth of 5 feet 

 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. i$a, I5&, 

 and I5c). 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 



