PRAIRIE PLANTS OF SOUTHEASTERN WASHINGTON 233 



depth of 12 or 13 feet, while most of them get the bulk of their 

 water from the second to the sixth foot of soil. ( 'consequently a 

 consideration of soil moisture at these depths is imperative for a 

 proper understanding of root environment. These deeper soil 

 water determinations (many to a depth of 8 feet) were taken at 

 intervals from December, 1912, to August, 1914. Samples were 

 taken in duplicate from separate holes. Figure 2 (solid lines) 



Fig. 2. 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 contenl of the 

 soil on December 13, 1913. The dotted lines indicate water contents on a nor, h- 

 east slope. 



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 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 indi- 



