AS INDICATED BY OSMOMETERS. 



75 



the results of this study will be presented. Finally, a test of the water- 

 supplying power of a soil in which a plant had become permanently 

 wilted will receive some attention. The experiments with water and 

 those with soil will again be presented together. 



For the two experiments where the instrument operated against 

 water, and for one test with 5 per cent soil (on basis of dry volume), 

 the average hourly rates and means are given in table 11, which con- 

 forms with table 10. The 15-minute rates are again suppressed, since 

 they show no new points. The temperature ranges for these tests 

 were approximately comparable within the group and with most of 

 the tests heretofore considered, being from about 27 to about 31 C. 

 The final means represent the rates after the first hour. 



The results shown in table 1 1 agree in general with the corresponding 

 ones of the series above presented, and require no special comment. We 

 shall now consider the three special soil tests made with osmometer C. 



TABLE 11. Average hourly absorption rates of osmometer C, operating against water and 

 against soil mixture containing 5 per cent of soil moisture (on basis of dry volume). 



*After first hour. 



It has been noted throughout the presentation of experimental 

 results that all soil tests and some water tests agree in showing unusally 

 high initial absorption rates, these rates tending subsequently to 

 decrease with more or less rapidity toward a lower rate, which was 

 long maintained in the case of the drier soils. It appears probable 

 that two sets of conditions may be operative in bringing about this 

 phenomenon. The first of these may be a set of conditions within the 

 osmometer, the second set seems to lie outside. 



What may be the causative factors inside the osmometer can not now 

 be determined. They may be related to changes in the membrane in 

 relation to its imbibed water (as through variations in tension between 

 the imbibed water and external water, brought about when the instru- 

 ment is emptied of distilled water and placed in active use with a sugar 

 solution upon one side). They may be related to some critical limit 



