RESEARCH METHODS IN STUDY OE 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 



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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 t hat soils of closely related origin 

 may be compared, as to their current conditions, on the basis of tho 

 amount of free or available water in each. This proposition, it will 



be remembered, the writers were unable to accept with reference to 



-oil- of unrelated origins, which gave rise to the need for (Ins whole 

 in\ e-t igation. 



