VOLUME LXII : NUMBER 1 
THE 
PeOTANICAL (GAZETTE 
SOLS 2 
MEASUREMENT OF THE SURFACE FORCES IN SOILS 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 217 
CHARLES ALBERT SHULL 
(WITH FIVE FIGURES) 
I. Introduction 
Many investigations of soil moisture have been made, especially 
during recent years, in attempts to learn something of its mechanics 
and its relations to plant growth. Ina general way the dominating 
importance of the soil water to plants has long been recognized; 
but notwithstanding the large amount of work done up to the 
present time, we still lack some of the most fundamental, elemen- 
tary facts regarding the physico-chemical relations of the water 
and soil. This is true generally of that region of soil moisture 
which lies between what is called the wilting coefficient of the soil 
and air-dry soil, and more particularly of that critical region 
immediately below the wilting coefficient. 
The discovery of semipermeable coats in seeds in recent years 
by Brown (4), SCHRODER (30), and others has made it possible to 
measure approximately the force with which the colloidal gels of 
the seed attract water. In a former paper (33) it was shown that 
by means of osmotic solutions whose forces are known the imbibi- 
tion force of a seed at any given moisture content from saturation 
to air-dry could be determined approximately. 
. Because of the rapid establishment of moisture squib 
relshions after disturbance in Xanthium seeds, this seed has been 
I 
