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 these 
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 similarly the 
contents which by the method just described are found definitely not 
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- 
DIAGRAM 1 
RELATION OF WILTING COEFFICIENTS 
TO 
SILT AND CLAY CONTENTS 
OF 
MICHIGAN SANDS 
2_ ol-foot samples containing little humus, 
x Surface samples with more or less humus 
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lation between the final wilting coefficients for jack and Norway pines 
on the one hand, and the combined silt and clay contents of the re- 
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 was 
different; but these, when decidedly lacking in humus, might give 
even lower values than the deep soils, probably on account of more 
thorough leaching. The results, as shown in diagram 1, indicate that 
if silt and clay were entirely eliminated, the sands might still possess 
a wilting coefficient of about 0.43 per cent. This is extremely close 
to the value for unfree water which Boiwoucos found to be almost 
constant in the case of quartz sand, regardless of the experimental 
conditions. 
The conclusion is therefore reached that, in the final struggle which 
determines whether the plant shall obtain sufficient water for its 
