THE USE OF “INSOLUBLE” SALTS IN BALANCED 
SOLUTIONS FOR SEED PLANTS 
B. M. DUGGAR 
Physiologist to the Missouri Botanical Garden, in Charge of Graduate Laboratory, 
Professor of Plant Physiology in the Henry Shaw School of Botany of 
Washington University 
In this paper it is proposed to give the results of several series 
of experiments designed primarily to determine the possible 
value of certain relatively insoluble salts in furnishing the nec- 
essary ions for the growth of seed plants. By means of such 
salts it will also be attempted to secure favorable combinations 
of the necessary ions. Throughout this discussion “insoluble” 
may be used in a very general sense, to include many salts soluble 
only to a comparatively slight degree, or with difficulty soluble, 
in water at from 15 to 25? C. 
It is well known that in the soil a relatively small part of 
the salts ordinarily designated mineral nutrients is present in 
soluble form. "There is, in general, a very considerable reserve 
or *unavailable" supply of the less readily soluble salts of such 
elements as K, Ca, Mg, Fe, S, and P. Nitrates are generally 
present only in low concentration and the surplus nitrogen 
supply is usually in the form of organic compounds. It has 
seemed to the writer eminently desirable to determine, there- 
fore, if à favorable nutrient solution for seed plants may not 
be arranged from combinations of some of these insoluble salts, 
thus in some measure imitating the chemical relations in the 
soil. 
In favor of this endeavor it might be argued that should this 
prove possible it would only be necessary to add to the culture 
vessel a surplus of the substances required. A small amount of 
that added would go into solution immediately and when an 
equilibrium were attained the absorption of any ions by the root 
would be compensated for by further solution of the substances 
furnishing these ions, and thus the equilibrium might be main- 
tained and the concentration kept fairly constant over con- 
siderable intervals. Obviously, it would be impracticable to 
furnish nitrate as an insoluble compound, since the nitrates of 
ANN. Mo. BOT. GARD., VOL. 7, 1920 
