20 



THE ECOLOGICAL RELATIONS OF ROOTS. 



Table 2. 



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



percentages. 



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

 The minus sign indicates water non-available for plant growth. 



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-killing 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 



