BoviE: NON-AVAILABLE WATER IN SOILS 291 
films. Therefore, it is important that we understand the condi- 
tions of equilibrium between the plant and this form of water. 
3. It is apparent that the isotonic values determined for sub- 
stances dissolved in free water do not necessarily hold for film- 
water. We cannot thoroughly understand the acquisition of water 
and food by land plants, or the results from fertilizer experiments 
until some of these values are known. Further, the conditions of 
equilibrium im film water must be determined for both toxic and 
“balanced” solutions, before we have reached a logical stopping 
place for these lines of research. 
4. The investigations should be carried out with carefully con- 
trolled experiments, in which the number of unknown factors is 
reduced to a minimum. Fundamental principles will scarcely be 
demonstrated by experiments on soils chosen at random in the 
field. Such soils contain too many unknown factors. Experience 
shows that experiments from soils from the same locality may not 
yield comparable results. The soil used should be of simple com- 
position, and its content known. We must have a number of 
simple standardized soils, of which samples can be duplicated. 
I have used a soil with comparatively few unknown factors, and 
one that is to be had in practically unlimited amounts. These 
experiments can be duplicated. 
5. Much of our knowledge of the relation of plants to the soil 
must be obtained by indirect methods. <A great deal of it must 
be worked out in the laboratory of the physical chemist. But all 
such results should be checked up by experiments with the plant 
itself, for the problem of the relation of plants to the soil is pri- 
marily a problem in botany, both inits inception and final solution. 
The greater part of this work has been done under the direction 
of Professor C. Stuart Gager, whose suggestions and encourage- 
ment have been invaluable in its prosecution. 
DEPARTMENT OF BOTANY, 
UNIVERSITY OF MISSOURI, 
Columbia, Mo. 
1. Bogdanhoff, S. Ueber das Verhalten der keimenden Samen zum 
Wasser im Allgemeinen und speziell zur Bodenfeuchtigkeit. Landw. 
Versuchs-Stat. 42: 311-366. 1893. 
2. Bovie, W. T. A plant-case for the control of relative humidity. 
Torreya 10: 77-80. f. I. 1910. 
