Rothamsted Symposium on Trace Elements 58 



Manganese is also able to reduce the absorption of iron from 

 a nutrient solution. The investigations of Johnson (11), Hop- 

 kins (8), ScHOLZ (22), and Pearse (20) showed that manganese 

 oxidizes iron in culture solution to the ferric state decreasing its 

 uptake. According to Kriel (14), as quoted by Bennet (1), an 

 excess of manganese in culture solution produces chlorosis by re- 

 ducing iron absorption. 



Table 14: Effect of manganese addition on the heavy 

 metal content of manganese-deficient peas: — 



Manganese given 



PER LITRE OP Content in kg dry matter 



NUTRIENT Roots Lcavcs 1-8 Leaves 9-18 



SOLUTION Cu Mn Fe Cu Mn Fe Cu Mn Fe 



What is the explanation of the action of copper and manganese 

 within the plant itself as well as on the iron content of the plant? 



Kliman (13) suggests that the plant takes iron, chiefly, if 

 not wholly, as ferrous iron. In my own experiments, iron was 

 given in the form of ferric citrate. It is, therefore, most probable 

 that the reactions now observed between heavy metals are to be 



Table 15: Relations between copper, manganese, and iron in plants. — 



Copper Manganese 



Deficiency Excess Deficiency Excess 



Vacuolar sap — Fe-deficiency Fe-excess Fe''"'' —y Fe'*"^"'' 



Protoplasm 

 (Chloroplasts) Fe-deficiency Fe-excess Fe-excess Fe-deficiency 



attributed mainly to oxidation-reduction reactions in the plant it- 

 self. 



Table 15 and Figure 6 illustrate some possible relations be- 

 tween copper, manganese, and iron in plants. 



Copper, as we have seen, accumulates particularly in the proto- 

 plasm. Delf (4) found that the movement of copper takes place 



