Tue Errect oF MANGANESE COMPOUNDS ON SOILS AND PLANTS 373 
salts and 0.02 per cent of manganese sulfate in one series, and 0.05 per 
cent of nutrient salts and 0.002 per cent of manganese sulfate in the 
other series. 
Tottingham and Beck (1916) reported increased yields of wheat grown 
in nutrient solutions containing smal! quantities of manganese chloride. 
Various views are held regarding the cause of the stimulation on the 
one hand and of the toxicity on the other. Loew and Sawa (1902-03) 
suggest that the stimulation by manganese is related to the oxidation 
of toxic substances within the plant leaf. They assert that certain noxious 
by-products are formed in the leaf, and that in reality sunlight retards 
growth. They state: “It is in the absence of light that growth 
proceeds and the products of the sun’s work are chiefly consumed.” 
Protoplasm oxidizes the carbohydrates formed, while the noxious by- 
products, probably members of the benzene group, are oxidized by enzymes, 
whose action is increased by the presence of manganese. 
Many investigators find that the action of enzymes is in some way 
related to the presence of manganese. Kastle (1910) writes at length 
on manganese in its relation to the oxidizing ferments. It has been 
shown by Bertrand, he states, that the oxidizing power of laccase (from 
lucerne) is associated with the manganese content. He regards this 
element as the co-ferment, or activator, of laccase, just as hydrochloric 
acid is the co-ferment of pepsin. The oxidation of organic compounds, 
such as hydroquinon, by the oxygen of the air, is accelerated by the 
presence ‘of manganese and varies with the form of the salt, being greater 
with the salts of the organic acids. These salts are “ most easily hydro- 
lyzable”’; thus, 
R’Mn + HOH = R” A, + Mn0. 
The manganous oxide formed is “ spontaneously oxidizable.”” In this 
oxidation, “ molecular oxygen is split into two atoms, one of which com- 
bines with the manganous oxide to form the peroxide, the other going to 
oxidize the hydroquinon ’’; thus, 
MnO + O. = MnO, + O, and 
C,H. (OH). “= O —— C.H:02 + HOH. 
In the presence of an acid, R’’H2 is unstable and is capable of oxidizing 
more hydroquinon. Thus the manganese salt is regenerated. ‘‘ Accord- 
ing to this conception the manganese would be the really active element 
