20 



THE ECOLOGICAL RELATIONS OF ROOTS. 



Table 2. 



In tables showing water-content it will be understood that the figure columns represent 



percentages. 





Depth of samples. 





Depth of samples. 



Date. 



to 4 inches. 



4 to 12 inches. 



Date. 



to 4 inches. 



4 to 12 inches. 





Wilting 



Wilting 





Wilting 



Wilting 





coefficient 12. 



coefficient 12.7. 





coefficient 12. 



coefficient 12.7. 



May 21 



19.5 



17.3 



July 31.... 



- 0.8 



0.1 



June 5 



- 2.5 



4.8 



Aug. 7 



9.5 



8.8 



June 10. . . . 



- 3.5 



3.8 



Aug. 15 ... . 



20:0 



13.8 



Jime 17 



3.5 



9.1 



Aug. 22 



- 2.2 



-2.7 



June 26 



16.5 



9.5 



Aug. 28 



- 1.7 



3.8 



July 1 . . . . 



1.3 



5.5 



Sept. 4.... 



13.1 



8.8 



July 8.... 



- 2.4 



2.0 



Sept. 12 



13.5 



5.3 



July 17.... 



9.5 



2.8 



Sept. 19 



2.0 



1.8 



July 24 



- 1.2 



0.3 









Table 3. — Available water-content of the prairie soil during 1917. 

 The minus sign indicates water non-available for plant grov.'th. 



Date. 



Depth of 

 sample, 

 to 6 

 inches. 

 Wilting 

 coefficient, 

 13.4. 



Depth of 

 sample, 

 6 to 12 

 inches. 

 Wilting 

 coefficient, 

 13.4. 



Depth of 

 sample, 



1 to 2 



feet. 

 Wilting 

 coefficient, 



15.4. 



Depth of 

 sample, 

 2 to 3 

 feet. 

 Wilting 

 coefficient, 

 14.5. 



Depth of 

 sample, 

 3 to 4 

 feet. 

 Wilting 

 coefficient, 

 16.1. 



Depth of 

 sample, 

 4 to 5 

 feet. 

 Wilting 

 coefficient, 

 16.1. 



Apr. 3 



May 6 



4.3 

 -2.9 

 4.9 

 -1.9 

 -1.7 

 -3.1 

 -5.3 

 1.6 

 7.0 

 2.1 



4.3 

 6.7 

 9.8 

 2.0 

 0.7 

 -1.7 

 -2.3 

 -1.3 

 0.5 

 1.7 



-2.6 

 2.2 

 8.1 



-1.6 

 -1.4 

 8.4 



-2.9 



-0.4 



July 9 



6.1 



4.3 



July 16 



2.1 



1.7 







July 23 







July 30 



-4.0 









Aug. 6 









Aug. 13 











Aug. 28 



July 24 (1916) 



-2.1 

 -0.9 

 -0.9 

 1.4 



-1.3 

 2.3 

 -0.7 

 -3.9 



-4.5 



-1.9 



Jan. 5 (1918) 



Mar. 26 (1918) 



3.3 

 7.2 



1.9 

 7.4 



0.6 

 -4.2 



2,1 

 -2.8 



On May 6 and again throughout the whole of July, no water was 

 available in the first 6 inches of soil. During late July and the first 

 week of August soil moisture was depleted to a point below the wilting 

 coefficient for a depth of 12 inches. On April 3 and again on August 28 

 no water was available at a depth of 1 to 5 feet. These results are 

 rather surprising, but an examination of the rainfall record shows that 

 during 1916 the precipitation was 5.5 inches below normal, while during 

 1917 it fell to 6.5 inches below. The dryness of the soil during 1916-17 

 was shown by an abnormal amount of winter-kilHng of trees and 

 shrubs. During July the rainfall was only 0.56 inch instead of the 

 normal 4 inches. The determinations on July 24 (1916) at 2 and 3 

 feet respectively show that the soil was very dry. It is interesting to 

 note in this connection that similar results were obtained in the 



