178 M. M. McCooL 



" 2. While strong solutions of manganese sulphate exert a toxic in- 

 fluence upon the growth of barley, very dilute solutions have a definite 

 stimulative effect." 



In another series reported by Brenchley, the nutrient solution 

 employed was about twice as concentrated as that in the former experi- 

 ment (unfortunately the exact concentration was not reported). In the 

 stronger nutrient solution the presence of manganese in the proportion 

 of 1 part per 10,000 of nutrient solution resulted in stimulation, the 

 toxicity of the manganese being thus reduced. 



EXPERIMENTAL STUDIES 



The WTiter has made experiments with manganese from time to time 

 since the autumn of 1910. The results of these experiments are presented 

 in this bulletin. The studies may be grouped as follows: 



I. The toxicity of manganese in (A) distilled water, (B) full nutrient 

 solution, and (C) soil cultures; and (D) the relation of previous conditions 

 of growth to toxicitJ^ 



II. The influence of light on toxicity' of manganese. 



■ III. The antidotal relations that exist between manganese and each 

 of the minerals calcium, potassium, sodium, and magnesium. 



Generally Canada field pea seedlings were employed, but in some 

 cases, specially mentioned, wheat seedlings also were used as indicators. 

 The manipulation and the method of experiment, unless otherwise specified 

 were the same as those described previously. 



Toxicity of manganese 



Manj^ substances at high dilution have a stimulating action toward 

 green plants, but at higher concentrations may be poisonous. Manganese 

 belongs to this class of substances. 



Manganese salts in distilled water.- — • The soluble salts of manganese 

 in distilled water are, of course, more toxic to Canada field pea seedlings 

 than is any nutrient salt. A solution of N/4000 MnCb is injurious, and 

 N/2000 MnClo prevents root growth entirely. The data presented 

 below were obtained from pea seedlings placed in pure solutions of manga- 

 nese chlorid: 



