2 BOTANICAL GAZETTE Ijuly 



chosen for a further investigation of the moisture relations of seeds, 

 with special reference to the moisture held by soil particles. The 

 main purpose of the work was to find some means of measuring 

 the force with which particles of soils of varying fineness retain 

 moisture at different degrees of dryness, and to obtain some more 

 definite knowledge concerning the amount of "back pull" occur- 

 ring in soils when the total moisture content is so low as to be 

 unavailable to growing plants. Special interest centered in the 

 conditions obtaining in the critical region at and just below the 

 wilting coefficient. 



This paper presents the principal results obtained during the last 

 three years. Since the osmotic method of measuring the internal 

 forces of seeds is obviously restricted in practice to such seeds as 

 have a perfectly semipermeable coat, a new method was attempted, 

 based upon a determination of the vapor pressure equilibrium 

 between seeds and osmotic solutions of varying strengths. This 

 method has the advantage of being applicable to all sorts of seeds, 

 regardless of the kind of testa present; but since von Schroder 

 (31) and Bancroft (2) have shown that colloids may not have 

 the same moisture relations to gaseous moisture that they have 

 to water itself, the values obtained by the vapor pressure method 

 have not been used as the basis of comparison with soils in this 

 work. The values for the internal force of seeds as determined by 

 osmotic solutions of various strengths will therefore be used as a 

 basis for comparing the moisture-holding power of fine soil particles. 



A number of soils have been used in the investigations, and it 

 is believed that the methods of measurement used here will prove 

 valuable in many kinds of soil moisture studies, since the deter- 

 minations, while giving excellent data as to the physical relations 

 of the soil moisture, yield at the same time results of considerable 

 physiological significance. The results are more valuable, therefore, 

 than purely physical determinations, because they can be inter- 

 preted in terms of plant activity. For, after all, it is the plant in 

 relation to its environment, not merely the environment, that we 

 need to understand. 



The work has been carried on in the Plant Physiological 

 Laboratory of the University of Kansas, and in the Hull Botanical 



