CONTENTS. 



Page. 



Introduction 7 



Wilting coefficient 8 



Wax-seal method for determining the wilting coefficient 10 



Essentials in determining the wilting coefficient 10 



Description of the method 10 



Composition of the wax seal 13 



Experimental error 14 



Comparison of the soil-moisture content at the wilting point and the death 



point , 16 



Effect of the age of the plant on the wilting coefficient 19 



Effect of environmental conditions on the wilting coefficient 22 



Humidity 22 



Light intensity 23 



Relation of soil-moisture content during growth to the wilting coeffi- 

 cient 24 



Wilting coefficients for different plants grown in a series of soils 25 



Relative influence of the soil and the plant on the wilting coefficient 33 



Relative wilting coefficients for different plants 34 



Comparison of the wilting coefficient for different plants by growing them simul- 

 taneously in the same pot 39 



Method for determining the wilting coefficient for plants having no definite 



wilting point 47 



Causes of variation in wilting-coefficient determinations 53 



Causes for determinations having a value less than normal 53 



Causes for determinations having a value greater than normal 55 



Indirect methods of determining the wilting coefficient 56 



Relation of the wilting coefficient to the moisture equivalent 56 



Additional data on the relation of the wilting coefficient to the moisture 



equivalent 59 



Application of indirect wilting-coefficient determinations to the interpre- 

 tation of field moisture determinations 61 



Other indirect measurements of the wilting coefficient 64 



Relation of the wilting coefficient to the hygroscopic coefficient 64 



Relation of the wilting coefficient to the saturation coefficient and to 



the moisture-holding capacity of soils 66 



Relation of the wilting coefficient to soil texture as expressed by 



mechanical analysis 68 



Graphical representation of the relationship between the wilting coefficient 



and the physical measurements of moisture retentivity 70 



Comparison of the accuracy of the indirect physical methods for deter- 

 mining the wilting coefficient 71 



Formulas showing relationships between physiological and physical 



measurements of moisture retentivity 72 



Subsidiary formulas 72 



Determination of the moisture equivalent 72 



Determination of the hygroscopic coefficient 73 



Determination of the moisture-holding capacity 73 



Determination of the maximum available moisture 73 



Summary 73 



Index 79 



230 5 



