1914] KELLEY—FUNCTION OF MANGANESE 225 
bring about stunted growth and might be sufficient to account for 
the difference in size of the plants from the two classes of soil. 
Studies on the solubility of these soils have shown the manganese 
to be slightly soluble in water, but markedly so in dilute organic 
acids. Phosphoric acid coming into solution in the soil moisture 
would tend to be precipitated by the manganese as manganese 
phosphate, a compound, which can be dissolved only with diffi- 
culty, and therefore the absorption of phosphoric acid would thus 
be hindered. 
Reference has already been made to the fact that certain organic 
substances exert appreciable influence on the rates of absorption 
of certain of the necessary elements. Here it is shown that a 
similar action is to be ascribed to manganese. How is this fact to 
be explained ? 
During recent years the protective action of salts shown to 
obtain in animal experiments by Logs (18) has been found to 
apply also to plants. 
OsTERHOUT (19) has shown from water cultures, for instance, 
that some of the essential elements may be toxic unless properly 
balanced by definite concentrations of certain other necessary 
elements. In other words, some at least of the essential inorganic 
elements seem to play both a nutritive and a protective rdle. 
Quite recently OsTERHOUT (20) has been able to throw considerable 
fi t on the mechanics of the protective action. By the use of an 
Ingenious device he determined the electrical conductivity of living 
Protoplasm, both before and after it was placed in solutions of 
ium and calcium chlorides, etc. The results show that the 
electrical resistance of the protoplasm becomes greatly reduced 
upen standing in sodium chloride solution, thus indicating that 
sodium had been absorbed. But when the protoplasm was placed 
i a solution containing sodium and calcium chlorides, of the same 
lonic Concentration, no such lowering of the resistance took place. 
alcium hinders, then, the passage of sodium through living pro- 
toplasm; and therefore must be looked upon as lowering the per- 
meability. OsreRHout has further shown this phenomenon to 
be Teversible, and therefore the presence of one salt may actually 
Cause an increase in the permeability to others. In certain instances 
