Effect of Manganese Compounds 



85 



wheat and peas. The intensity of the colour reaction of the oxidising 

 enzyme of the manganese plants was found to exceed that of the control 

 plants, at least with regard to those leaves on the manganese plants 

 which had turned a yellowish colour. 



Loew and Sawa (1902) obtained an initial increase of growth with 

 barley and soy beans in nutritive solutions + -01 % ferrous sulphate + 

 ■02 % manganese sulphate, but this initial stimulation was followed by 

 depression. These authors support Aso's contention that manganese 

 exerts both an injurious and a stimulative action upon plants, and that 

 the promoting effect is still observable with manganese compounds in 

 high dilution, while the injurious effects disappear under this condition. 



1000 100 10 



2 1 -2 



1=1:10,000,000 



Pig. 17. Curve showing the mean value of the dry weights of ten series of harley plants 

 grown in the presence of manganese sulphate and nutrient salts. (Feh. 5th — March 

 29th, 1909.) 



The Kothamsted experiments with barley show a decided stimulation 

 with 1/100,000 MnSOi and less. Care was taken to utilise sublimed 

 FeClj to avoid error due to the introduction of manganese into the 

 control solution through the agency of this salt. It is interesting to 

 notice that concentrations that are weak enough to stimulate the 

 vegetative growth still show a depressing action in that they retard the 

 ripening of the grain, a fact which supports Loew and Sawa's contention 

 that manganese exerts both a toxic and a stimulative action at one and 

 the same time, the balance showing itself according to the concentration 

 (Fig. 17). In the later experiments the plants were not allowed to form 

 ears, but similar results were obtained, except that when dealing with 



