52 
THIRTEENTH REPORT. 
BOIL AND SOIL PROBLEMS FROM STANDPOINT OF BOTANIST. 
w. h' brown. 
The soil problem from the standpoint of the Botanist or Plant 
Physiologist may naturally be divided into two parts: 
1. The influence of the soil on the plant. 
2. The influence of the plant on the soil. 
In dealing with the first part of this problem, the methods used by 
the Plant Physiologist have usually not differed greatly from those 
employed by the Soil Physicist or Chemist, since they have usually 
consisted in an attempt to correllate the chemical or physical factors 
of the soil with either the total or dry weight of the plant produced. 
This has been largely the result of the fact that plant physiology is a 
comparatively new science and that certain general relations had to be 
established before the underlying physiological problems could be at- 
tacked. While from a physiological standpoint, such methods could 
liardlv more than scratch the surface thev have nevertheless vielded 
valuable results. For example it has been found that certain elements 
are necessary for plant life and that the plant can obtain these from 
certain chemicals and not from others, that some combinations of chem- 
icals are favorable to growth, that a certain texture or water content 
of the soil is necessary for some plants and that these conditions vary 
for different species. In much of the work along this line, however, the 
mistake has been made of dealing with a complex of factors rather than 
with individual ones, with the result that the experiments could not be 
repeated or fundamental conclusions, which would serve as a basis for 
future work, derived from them. For example, the addition of certain 
things such as fertilizers or organic matter to the soil has often been 
treated as an experiment with a single factor even though the things 
added have been complex and have changed the physical and chemical 
properties of the soil and influenced the microorganisms in it. Even 
when individual factors have been dealt with, the relation of these to 
others has frequently been so complex that some factors have either been 
ignored or overlooked, with the result that later work has proved the 
first conclusions either inadequate or erroneous. A good example of 
this is afforded by the non-available water content of the soil which is 
the water remaining in the soil after the plant has withered and died 
because it could not obtain sufficient to supply that lost by evapora- 
tion, and to maintain life. The amount of this non-available water 
has been found to vary with different soils and plants and so without 
taking into consideration the atmospheric conditions it has generally 
been stated that it is constant for a given soil and plant. Experiments 
carried on in Arizona have however, shown that similar plants of Vicia 
fnba growing in the same soil, would wilt when Hie soil contained any- 
where from 8 to 35% of water, depending upon the amount of evapora- 
tion. As will be pointed out later changes in the internal conditions of 
the plants also affect the amount of non-available water. While it is 
