MISSOURI BOTANICAL GARDEN BULLETIN 67 
the time seem to have the remotest connection with problems 
of human diseases, yet this discovery was undoubtedly the 
most important single contributing impulse leading to the 
discovery of the réle of micro-organisms in diseases. Pfef- 
fer’s measurements of the osmotic pressure of solutions of 
cane sugar and De Vries’ studies of the pressures in plant 
cells threw fundamental light upon the movements of sub- 
stances and solutions in all tissues as well as led to the de- 
velopment of new laws in physical chemistry. Facts derived 
from a study: of the nutrition of micro-organisms have not 
infrequently been made the basis of improved methods of 
feeding in the case of certain human diseases. 
A present day department of botany with complete facil- 
ities for research in all fields has no exact counterpart on the 
animal side. Frequently all phases of animal physiology, 
pathology, and chemistry are included in the departments 
of the medical school, but in plant work these important 
phases are all grouped together as one subject along with 
the older subdivisions of botany. It is, therefore, obvious that 
the work is comparable to that of a group of research depart- 
ments. 
An Electrical Method for Determining Root Excretion.— 
Visitors to the Garden have seen peas and other plants 
in the experimental greenhouse growing with their roots in 
tumblers of solutions and they have doublons wondered what 
the object was in growing plants in that manner. In ex- 
planation it may be said that the water culture, or solution 
method, is indispensable for many purposes, and Mr. M. C. 
Merrill, Research Assistant, has employed it in the investiga- 
tion described below. 
To determine what mineral nutrients, or inorganic salts, 
are absolutely necessary or desirable for the growth of plants, 
the method is to place the roots of the seedling plants to_be 
tested into pure distilled water to which have been added 
various salts. By withholding each substance, or salt, in 
turn from similar cultures under observation at the same 
time, it can be found which are essential, or what happens 
when the solution is variously ‘“unbalanced.”” Obviously, soil 
cultures would not serve the purpose. Now the roots, or more 
especially the root hairs on the younger parts of the roots, 
absorb water and salts in solution from the medium in which 
they are growing, and this important process of absorption, 
or endosmosis, as it is termed, has necessitated much study. 
Less attention has been given to the ae process,—which 
may be a very important one, too—that of the outflow of 
salts and other substances from the roots into the surround- 
ing medium, a process designated as exosmosis. One com- 
