224 



BOTANICAL GAZETTE 



[SEPTEMBER 



soil conditions approximately similar to those of the preceding asso- 



ciation. 



hickory 



com 



pleteness, especially since the record for 19 12, owing to a series of 



srmen 



here is a clay with an admixture of grav 

 manner from the sand in its moisture 



shown by 



coefficients 



Although the water 



Fig. 22. — Graphs showing the range of soil moisture in the oak-hickory forest for 

 191 1 ; the heavy line at 7 . 5 cm. and the light line at 25 cm. depth; wilting coefficients 

 represented by broken lines. 



depths of 7 . 5 cm. and 25 cm. The fluctuations in the soil moisture 

 are great, particularly at 7.5 cm. (fig. 22). 

 content of the soil at 35 cm. once falls below the wilting coefficient, 

 the average amount of growth-water for the midsummer weeks is 

 considerable (table III), much greater in fact than in any preceding 

 association, indicating decidedly more mesophytic soil conditions. 

 It may be noted that the wilting coefficients now given for this 

 and the succeeding association differ slightly from those formerly 

 published. This is due to their redetermination by more careful 

 methods, particularly to the use of the indirect method. 



