RESEARCH METHODS IX STUDY OF FOREST ENVIRONMENT. 119 
2. The osmotic equivalent of the soil is almost wholly dependent 
upon the solutes present, and among soils of one general type, in 
which the ingredients are conducive to the creation of solutes at a 
definite rate, and their free transfer from one point to another, a 
given osmotic equivalent represents a fairly constant amount of 
free water plus a variable amount of unfree water, depending on 
the quantity of clay, humus, etc., in each sample. 
3. In such a group of related soils the wilting coefficients may 
have some fairly constant relation to the capillary moistures or mois- 
ture equivalents, because both measures are affected by the water- 
holding power of the colloids in large part ; but a capillary measure 
DIAGRAM IO 
OSMOTIC AND CAPILLARY RELATIONS 
SOILS FROM DIFFERENT DEPTHS AT COMMON POINT 
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of the condition of the soil water is not alone a safe criterion as to 
its osmotic condition or availability at points considerably above 
the wilting coefficient. 
It is believed that these conclusions are essentially in accord with 
those of Bouyoucos (106) and Hoagland (127), as derived from 
their study of freezing points and osmotic pressures. Probably this 
conception of the factor affecting availability is of greatest value 
in explaining the poor growing conditions of undrained soils and 
the great preference of trees for those which are well drained. It is 
also of importance in indicating that soils of closely related origin 
may be compared, as to their current conditions, on the basis of tha 
amount of free or available water in each. This proposition, it will 
be remembered, the writers were unable to accept with reference to 
soils of unrelated origins, which gave rise to the need for this whole 
investigation. 
