182 



M. M. McCooL 



nutrient solution, respectively, are much more resistant to the poisonous 

 influence of manganese than are those that are transferred from germinating 

 pans and placed immediately in solutions of manganese. The nature of 

 the medium used in this preliminary treatment — that is, whether dis- 

 tilled water, tap water, or full nutrient solution — has no visible effect 

 on the resisting power of the plants as subsequently subjected to man- 

 ganese treatment. In these experiments the roots were carefully rinsed 

 with distilled water when they were removed from the tap water and the 

 full nutrient cultures. The data, which are arranged in the following 

 table, were taken five days after the plants were transferred to the solu- 

 tions of manganese: 



TABLE 4. Toxicity op Manganese after Ten Days Growth in Various Media 



Ten days 





Ten days 





Ten dajs in 





in distilled 

 water, 



Condition 



in tap 

 water, 



Condition 



full nutrient 

 solution, 



Condition 



then in 





then in 





then in 





N/25 MnCl2 



Dead 



N/25 MnCh 



Dead 



N/25 MnCl2 



Dead 



N/50 MnCU 



Dead 



N/50 MnCU 



Dead 



N/50 MnCl2 



Dead 



N/75 MnCh 



Dead 



N/75 MnCl2 



Slight growth, 

 dead 



N/75 MnCl2 



Dead 



N/100 MnCl2 



Slight growth, 



N/100 MnCl. 



Slight growth, 



N/100 MnCK. 



Slight growth, 





dead 





dead 





dead 



N/200 MnCl2 



Growing 



N/200 MnCh 



Growing 



N/200 MnCl2 



Growing 



The lethal concentration (N/75) of manganese is practically the same 

 for the plants that have been grown in the various media. A comparison 

 of the data in the above table with those in Table 1 (page 179) brings 

 out the fact that plants which have been grown for ten days in either 

 distilled water, tap water, or full nutrient solution are approximately 

 twenty-five times less sensitive to manganese ions than are seedlings 

 which are placed immediately in pure solutions of manganese. 



Influence of light on the injurious action of manganese with respect to 



^plants 

 Certain investigators have indicated that the juice of yellow leaves — 

 those that exhibit chlorosis resulting from the presence of excessive amounts 



