COMMEUCIAL FJERTILIZERS 531 



cent of Mn304. Sullivan and Robinson^ examined 

 twenty-six American soils and found the content of MnO 

 to vary from 0.01 to 0.51 per cent, the average being 

 0.071 per cent. 



Manganese is a universal constituent not only of soils, 

 but likewise of plants grown under natural conditions; 

 in plants the quantities present vary much more than in 

 soils, and range from a few tenths of one per cent to nearly 

 one-half of the total ash. However, plants may be pro- 

 duced in water cultures or other media in which apparently 

 no manganese is present and a normal growth and fructi- 

 fication will follow. It is evident, therefore, that any 

 benefit to plant growth that may accrue through the 

 addition of manganese to the soil is not due to its function 

 as a nutrient material in the sense in which nitrogen, 

 potassium, and phosphorus act in that capacity. 



450. Physiological r61e of manganese. — It was the 

 discovery by Bertrand ^ of the existence of manganese in 

 the oxidizing enzymes of plants and of its function in 

 stimulating the oxygen-carrying power of these catalytic 

 agents that suggested its use as a stimulating agent in 

 crop production. In water cultures a very dilute solution 

 of manganese salts increases plant growth, but beyond a 

 very low concentration its effect is toxic. Plants differ 

 widely in their response to manganese, with respect both 

 to stimulation and to injury. A certain concentration 

 may be stimulating to one plant and toxic to another. 



Experiments in the application of manganese salts 



1 Sullivan, M. X., and Robinson, W. 0. Manganese as a 

 FertiHzer, U. S. D. A., Bur. Soils, Circ. 75. 1912. 



2 Bertrand, G. Sur FAction Oxydante des Sels Manganeux 

 et sur la Constitution Chemique des Oxydases. Compt. Rend. 

 Acad. Sci. Paris, Tome 124, pp. 1355-1358. 1897, 



