SOILS i AND M A NUKES 



371 



Mr. Ingle {Sutherst and Ingle, 1) concludes that for the pre- 

 sent it will be safer to assume that manganese exerts a "tonic' 

 action, and that its application to a soil must not be regarded 

 as at all an efficient substitute for the plant-food required, and 

 usually supplied by means of artificial manures. In other 

 words, it is probably better regarded as a medicine than as a 

 food. 



Russel (2) observes that manganese is considered by 



CHAP. 

 VIII. 



Fig. 12S. — Effect of manganese compounds on maize ; A, Effect of 

 manganese dioxide. 



Bertrand (1) to be a constituent of oxidases, and, therefore, 

 necessary to the plant ; minute traces only are required, larger 

 quantities being harmful. A number of field experiments 1 have 

 shown that manganese salts may act as manures. Bertrand 

 classes them as " engrais complementaires". 



■Numerous Japanese experiments are recorded in the Bull. Coll. Agric, 

 Tokyo, 1906 et seq., and Italian experiments in the Studi e Ricerche di Chimia 

 Agraria, Pisa, 1906-8. 



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