196 



BOTANICAL GAZETTE 



[march 



While after protracted droughts and probably also after 

 extremely wet periods the moisture conditions in the subsoil are 

 quite uniform, they vary much from place to place under more 

 normal weather conditions, as illustrated by table IX. 



TABLE VII 



Moisture conditions in western Nebraska in May 191 2, after wet 



winter and spring 



Computations from data of Shantz and of Burr 



The only data reported by other investigators that may be used 

 for comparison with our own appear to be those secured by Shantz 

 at Akron, Colorado, in 1909, and by Burr at North Platte, 

 Nebraska, in 191 2. While neither of these authors reports the 

 hygroscopic coefficients of the soils, each gives the wilting coeffi- 

 cients for a representative set of samples, these having been com- 

 puted from the determined moisture equivalents. From these 

 data we have computed the hygroscopic coefficients by means of 

 the Briggs-Shantz formula (6, p. 65) : hyg. coef. = wilt. coef. X0.68. 



