WAX-SEAL METHOD FOR DETERMINING WILTING COEFFICIENT. 19 



when the total water content is known. This could not be deter- 

 mined directly by means of death-point observations, but would 

 require a correction term more or less dependent upon the plant 

 used. 



EFFECT OF THE AGE OF THE PLANT ON THE WILTING COEFFICIENT. 



In making wilting-coefficient determinations it is much more con- 

 venient to use seedlings than old plants. The question then arises 

 as to whether determinations made with seedlings as indicators 

 represent the moisture content of the soil corresponding to the wilting 

 point of more mature plants. The determinations given in Tables V 

 and VI were made with reference to this point. 



A series of experiments with Kubanka wheat plants, six soils in 

 each series, using plants of three different ages, is given in Table V. 

 The actual wilting-coemeient determinations for each soil are given, 

 together with the ratio of each individual determination to the mean 

 of each soil. The ratios indicate a slightly higher wilting coeffi- 

 cient for the younger plants, the means being 1.01 for plants 20 to 

 30 days old, 0.99 for plants 75 to 80 days old, and 0.98 for plants 

 104 days old. This is what would take place if the concentration of 

 the leaf-cell contents increased with the age of the plants. The same 

 effect would, however, be brought about by the more uniform root 

 penetration in the case of the older plants, or by an increase in woody 

 tissue in the leaves which would tend to retard the appearance of 

 wilting. Furthermore, when the differences are considered in con- 

 nection with their mean probable errors it becomes evident that the 

 influence of the age of the plants upon the wilting point is very 

 slight. 



Table V. — Effect of the age of wheat plants on the wilting coefficient. 





Wilting coefficients of plants at stated ages. 



Soil number. 



20 to 30 days. 



75 to 80 days. 



104 days. 





Actual. 



Ratio, 

 actual to 

 average. 



Actual. 



Ratio, 

 actual to 

 average. 



Actual. 



Ratio, 

 actual to 

 average. 



1 



f 0.86 

 1 .88 

 I 1.00 

 [ .80 



f 2.5 

 2.7 

 2.8 

 2.6 

 2.7 

 2.7 

 2.6 

 2.6 

 2.5 

 2.6 

 2.4 

 2.7 

 2.6 



1.00 



1.00 



1.16 



.93 



.97 

 1.04 

 1.08 

 1.00 

 1.04 

 1.04 

 1.00 

 1.00 



.97 

 1.00 



.93 

 1.04 

 1.00 



0.80 

 .87 



0.93 

 1.01 



0.78 

 .SS 



0.91 

 1.02 















2.7 



1.04 



2.7 



1.04 







L 



































2 







































































230 



