VOLUME L.KII NUMBh-K I 



LIBRARY 

 NEW YORK 

 BOTANICAL 



THE Garde* 



Botanical Gazette 



JULY 1 916 



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. In a 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 equilibrium 

 , relations after disturbance in Xanthium seeds, this seed has been 



