RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 69 



standard temperature of —4° C., and when the process was repeated 

 on the same sample several times. Without going further into th< 

 details, which are readily available in the original article, one more 



fact should be mentioned, namely, that the moisture contents at which 

 various soils fail to show definite freezing points, and similarl} the 

 contents which by the method just described are found definitelj Dot 

 to freeze, bear a close relation to the wilting coefficients of the same 

 soils. 



Directly bearing on the point as to the part played by the colloidal 

 masses of the soil, Bates (105) found, for eight samples of Michigan 

 and Nebraska sand, each taken at a depth of 1 foot, and consequently 

 showing a maximum of 2 per cent humus, that there was a Linear re- 



lation between the final wilting coefficients for jack and Nor* ay pines 

 on the one hand, and the combined silt and clay contents of the i 

 spective soils on the other. The latter varied from 0.3 to 6.4 per 

 cent. The behavior of surface soils with larger humus contents s as 

 different; but these, when decidedly lacking in humus, might gi 

 even lower values than the deep soils, probably «... account ol more 

 thorough leaching. The results, as shown in diagram 1 . indicate 

 if silt and clay were entirely eliminated, the sands might still poss< 

 a wilting coefficient of about 0.43 per cent. This is extremely 

 to the value for unfree water which Bouyoucos found to be almos 

 constant in the case of quartz sand, regardless of the experimental 



conditions. , _ , , , i 



The conclusion is therefore reached that, in the final struggle which 

 determines whether the plant shall obtain sufficient water for 



