KESEAECH METHODS IN STUDY OF FOREST ENVIRONMENT. 79 
The figures resulting from the above computations for the mois- 
ture of the soil in soil wells may be tabulated on the " Soil Moisture '" 
form in the columns headed " Sample. Tl." The ratio which has 
been determined between the moisture of the soil in the well and that 
of the native soil at same depth, and the computed moisture of the 
surrounding soil, or the moisture figure read directly from curves, 
may also be entered for each date. If the native soil moisture is 
directly determined by sampling, only the third column under each 
depth will be used. Space is also provided on the " Soil Moisture " 
form for any computations which it is desired to make, either cur- 
rently or after obtaining the monthly means; such as, for example, 
the percentage of available moisture, the availability, or the various 
percentages on a volume basis. Appropriate headings may be sup- 
plied. 
Determination of Nonavailable Moisture. 
The method of soil wells does not attempt to standardize soils for 
different localities, which could only be done thoroughly by using 
soil from one source in all soil wells. Nor is it desirable that soils of 
different localities should be compared on the same physical basis, 
since this physical basis of itself determines quite largely the mean 
water content of the soil and its attraction for a given species. It is, 
however, necessary before different sites and localities may be satis- 
factorily compared as to their soil moisture that it should be known, 
at least approximately, at what points they become physiologically 
dry, either for plants in general or for plants of a given species. 
Briggs and Shantz (114), it is true, after an exhaustive study of this 
subject which has cleared the way for many other investigations, 
summarize in part as follows : 
The results of this investigation have led us to conclude that the differences 
exhibited by plants in this respect are much less than have heretofore been 
supposed, and are so small as to be of little practical utility from the standpoint 
of drought resistance. As compared with the great range in the wilting coeffi- 
cient due to soil texture, the small differences arising from the use of different 
species of plants in determining the wilting coefficient become almost insig- 
nificant. 
Expressing this difference numericalty, it is said : 
Taking 100 to represent the average wilting coefficient, the different species 
tested (except Colocasia and Isoetes) give an extreme range from 92 for Japan 
rice to 106 for a variety of corn. 
From these experiments and conclusions the impression has grown 
up that all plants are capable of extracting the moisture of the soil 
to essentially the same basic point. Shantz may be quoted as say- 
ing that there was no intent to convey this impression, and experi- 
ments to be described later will show 7 that as between tree species 
