14 
Research Bulletin No. 3 
field — the average of the first 4 feet in each case — stating in 
each case the percentages of total, hygroscopic, and free water. 
Hilgard, as pointed out above, had recognized in the hygro- 
scopic coefficient an index of the heaviness of soils — the expres- 
sion, in a single value, of the texture of the soil — thus anticipating 
by fifty years the view of Briggs and McLane 1 as to the desir- 
ability in soil classification of a single-valued numerical term ex- 
pressing a common physical property of agronomic importance. 
LATER STUDIES ON THE N ON AVAILABLE WATER AND ON THE RELATIVE 
HYGROSCOPICITY OF SOILS. 
Gain, 2 using Erigeron canadensis, Lupinus albus, and Phase- 
olus vulgaris, allowed the plants, in porous earthenware pots, to 
wilt and then determined the moisture content of the soil. He 
used six different soils of which he had determined the "coeffi- 
cient of hygroscopicity according to the method of Schubler." 
He found rather irregular differences for the different plants but 
concluded that different plants behave in much the same man- 
ner as regards resistance to drouth. 
Soil hygroscopicity* Water content when P lants wUted 
Per cent 
Heath soil 9.26 to 11.50 
Clay 1.75 7.73 to 11.10 
Humus 6.0 5.92 to 6.95 
Calcareous sand f 0.15 2.90 to 5.23 
Garden soil 2.6 1.79 to 2.82 
Silicious sand 0.0 0 33 to 0.76 
* Gain, following Schubler's example, reported this as the weight 
of water absorbed by 1,000 grams of soil. To make it conformable with 
the other data the writer has changed it to a percentage basis. 
Mitscherlich 3 carried out a series of experiments similar to 
those of Heinrich, but allowed the plants to remain undisturbed 
until they died, when he determined the moisture content of the 
soil. Oats, white clover, red clover, and white mustard were 
grown on six soils whose hygroscopicity had been very accurately 
determined by exposure to an atmosphere in equilibrium with a 
10 per cent sulphuric acid solution. He concluded that plants die 
as soon as they have removed all except the hygroscopic moisture, 
1 Briggs, L. J., and McLane, J. W. Moisture Equivalent Determinations 
and Their Application. Proc. American Society of Agronomy, vol. 2, 1910, 
p. 138. 
2 Gain, M. E. Action de l'eau du sol sur la vegetation. Revue generale 
de botanique, vol. 7, 1895, p. 71. 
3 Mitscherlich, A. Landwirthschaftliche Jahrbucher. 1901, p. 410. 
