180 



M. M. McCooL 



A study of the preceding table and of Fig. 9 reveals some interesting and 

 unusual phenomena. The top growth of the seedlings amounts to only- 

 one centimeter in N/50 MnCl2, nutrient 

 solution being the solvent. In N/200 the 

 length of stems is reduced one half, whereas 

 the length of roots in N/50 is greater than 

 in the control. The main roots are longer, 

 but the laterals are shorter and less numerous, 

 than those on the control plants. The 

 presence of N/100 MnClo has very little 

 influence on the root development. 



Chlorosis of the leaves is the first indi- 

 cation of an overdose of manganese. The 

 stem and leaf development of seedlings in 

 N/300 to N/500 is normal for the first ten to 

 fifteen days; at about the end of this time the 

 green color begins to fade. In the stronger 

 solutions, as in N/50 to N/200, chlorophyll 

 The leaves in these cultures are chlorotic when 



Fig. 9.— Toxicity of MnCU 



1. N/50 MnCl2 in nutrient solution 



2. Control, full nutrient solution 



does not form normally. 



they appear and they soon cease growing. 



Manganese salts in soil cultures. — Much interest has been mani- 

 fested in the stimulating action of manganese when applied to soils, cs 

 evidenced by the numerous investigations reported. On the other hand, 

 studies of the poisonous action of manganese in soils are fewer in number; 

 therefore the toxicity of this ion has been considered of sufficient impor- 

 tance for further investigation. 



In order to determine the toxic action in soil, cultures were made up 

 as indicated in Table 3. One thousand grams of air-dry sandy loam was 

 placed in paraffined pots. To each of these pots was added a solution of 

 MnCl2 (330 cubic centimeters), as given in the table. Melted paraffin 

 was poured over the surface of the soil, and roots of pea seedlings were 

 inserted through holes in the paraffin into the soil below. In general the 

 results obtained are similar to those derived from the full nutrient solutions. 



The injurious action of manganese with respect to peas in soil cultures 

 is manifested mainly toward the tops; only relatively concentrated solu- 

 tions are harmful to the roots of the above plants. When a strong dose 

 of manganese (330 cubic centimeters of N/10 MnCl2 or MnS04) is applied 



