1914] KELLEY—FUNCTION OF MANGANESE 215 
The toxic effect above mentioned usually manifests itself by a 
dying-back of the growing tips and the yellowing of the leaves. 
Loew and Sawa (5) hold that the activity of the oxidizing enzymes 
of plants may become excessive under the influence of sufficiently 
great amounts of manganese, resulting in the auto-oxidation of 
the chloroplastids, thus destroying the green pigment. SALOMONE 
(10), on the other hand, found evidences of plasmolysis in wheat 
that had been fertilized with manganese dioxide at the rate of fifty 
kilograms per hectar. BRENCHLEY (11) also observed a_ toxic 
action from manganous sulphate when it was applied in the very 
low concentration of one part per one hundred thousand parts of 
culture solutions. When it is remembered, however, that many 
plants vegetate normally in culture solutions varying rather widely 
in ionic-concentration, without showing evidences of plasmolysis, 
in other words, the ionic-concentration of the cell sap considerably 
exceeds that of ordinary culture solutions, it seems improbable 
that the addition of such small amounts of manganous sulphate 
would produce plasmolysis as a direct effect. 
From the foregoing brief résumé? of the experiments on this 
question, it will be seen that two different sets of views have been 
held by which the action of manganese on soils and plants has 
been explained. These may be briefly stated as follows: (1) man- 
§anese stimulates the necessary oxidations going on in soils and 
plants through the activation of the oxidizing enzymes, etc.; 
(2) the application of soluble manganese brings about plant stimu- 
lation by rendering soluble, and therefore making available, the 
essential plant food of soils. 
Under the first named of these theories may be included the 
stimulated oxidations, in both soils and plant tissues, the former 
Probably being referable to the action on certain microorganisms, 
as well as on soil catalysis, while the latter has to do with the physio- 
logical processes within the cell. Viewed in the light of the last 
named theory, the effects of manganese on plants are considered 
to be indirect and due to its increasing the solubility of the mineral 
Constituents of soils. 
ae more complete bibliography of literature dealing with this subject will be 
n @ paper by the writer published as Bulletin 26, Hawaii Experiment Station. 
