2 BOTANICAL GAZETTE [JULY 
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. 
e work has been carried on in the Plant Physiological 
Laboratory of the University of Kansas, and in the Hull Botanical 
