30 BOTANICAL GAZETTE [JANUARY 
when exposed in a saturated atmosphere. Theres is consequently 
nothing definite or reproducible about such d tions, unless 
the conditions under which the measurements were made are also 
known, and any ratio derived from such measurements is likely to 
give misleading results when applied to other determinations. 
THE RELATION OF THE WILTING COEFFICIENT TO THE SATURATION 
COEFFICIENT AND THE ‘‘MOISTURE HOLDING 
CAPACITY’ OF SOILS 
The saturation water content or the saturation coefficient is the 
percentage of water held in the soil when all interstitial space is 
filled with water. The “moisture holding capacity” is the per- 
centage of water a soil can retain in opposition to the force of gravity 
when free drainage is provided. This is dependent upon the height 
of the soil column employed, diminishing as the height of the column 
is increased.‘ When the soil column is made very short, for 
example 1 cm. in height, the two determinations are practically 
identical. Both are greatly influenced by the packing and the 
granulation of the soil, so that determinations are subject to wide 
variation in the hands of different observers. 
In the accompanying table (table IV) the wilting coefficients of 
a series’? of soils are compared with the moisture holding capacity. 
Following Hitcarp,” the latter determinations were made with a 
soil column 1 cm. in height, with free drainage. 
The moisture holding capacity of the soils used in the comparison 
ranged from 23 to 71 per cent. In this case the ratio between the 
moisture holding capacity and the wilting coefficient is not constant. 
However, an approximately constant relationship is obtained if the 
moisture holding capacity is first reduced by 21. The ratio of the 
moisture holding capacity less 21 to the wilting coefficient is shown 
in the last column of the table. The mean ratio for the 15 soils 
% HILGARD, E. W., and Loucnrince, R. H., Rept. Calif. Sta. 1 
Brices, L. J., Mechanics of soil moisture. U. S. Dept. Agric., Div. Os Soils, Bull. 
to. 1897. 
7 In this work it was not possible to secure samples of all the soils used in the 
preceding experiments. 
8 HILGARD, E. W., Soils. 1906, p. 200. 
