Relations of Manganese and Other Cations 183 



of manganese — contains more active oxidases than does the juice of 

 normal leaves. . 



Loew and Sawa (1903), who found that manganous sulfate in certain 

 amounts is injurious to barlej^, state: " Manganese exerts in moderate 

 quantities an injurious action on plants, consisting of the bleaching out 

 of the chlorophyll. The juice of such plants shows more intense reaction 

 for oxidases and peroxidases than the healthy control plants." 



Kelley (1908) has pointed out that the leaves of pineapples grown on 

 soils high in manganese content give more distinct reactions for oxidases 

 with guaiacum and aloin than do the leaves from plants grown on soils 

 containing small amounts of manganese. The writer is not able to state 

 positively that the yellow color of the plants is brought about by actual 

 oxidation of the chlorophyll. 



It was noted in preliminary experiments that the manganese ion is 

 especially injurious to plants grown in intense light. Later studies, from 

 experiments conducted in cloudy weather, showed that the harmful action 

 of manganese is retarded somewhat when the plants are grown under 

 the lesser light intensity. 



Full nutrient cultures were made in duplicate, to which varying amounts 

 of manganese were added. One set of cultures remained in the light, 

 the other was placed in a darkened aerated chamber; otherwise the con- 

 ditions were as nearly the same as could be readily maintained. (No 

 apparatus was at hand at the time with which the relative humidity 

 could be regulated. This factor therefore was not controlled.) The 

 results obtained from these experiments appear in Table 5, in Fig. 10, 

 and in the discussion following. 



In order to determine more definitely the influence of light on the toxic 

 action of manganese, experiments were made in which plants were kept 

 on the one hand in darkness and on the other hand in normal light. The 

 results are given in Table 5. 



It is perfectly clear that manganese is far more injurious to the tops 

 of plants grown under ordinary greenhouse conditions than it is to those 

 grown in darkness. In culture 1, for example, the tops of the plants 

 were dead at the close of the experiment, while those in culture 2 were 

 alive although the leaves were very small and the stems were greatly 

 injured. The lower parts of the stems of the plant in the latter culture 

 were somewhat darkened, as shown in Fig. 10. The leaves of the seed- 



