Toxicity of Various Cations 



203 



Toxicity of potassium 

 Potassium is appreciably more toxic than calcium, but less injurious 

 than the other ions that the writer has studied. As is the case with cal- 

 cium, the injury is reduced when potassium is present in full nutrient 

 solution and in soil cultures. Slight elongation of tops occurs in solutions 

 composed of N/10 KCl, but no appreciable root growth appears in solu- 

 tions stronger than N/50 KCl. Cameron and Breazeale (1904) obtained 

 similar results from other substances; for instance, they found that " the 

 concentration required to kill a seedling or disorganize an entire radicle 

 varies widely from that required to completely hinder any growth or 



elongation, or that which will permit some elongation " 



The results of the writer's studies appear in Table 2: 



TABLE 2. Experiment with Wheat and Pea Seedlings, Continued for Ten Days. 



Data for Ten Plants 





Pea 



Wheat 



Composition of solution 



Increase 



in length 



of tops 



(centimeters) 



Increase 



in length 



of roots 



(centimeters) 



Increase 



in length 



of tops 



(centimeters) 



Increase 

 in length 

 of roots 

 (centimeters) 



Distilled water as the 

 solvent 

 N/5 KCl 







0.25 

 0.50 

 • 1.00 

 3.00 

 6.00 

 6.00 





 

 

 

 Slight 

 7.50 

 7.00 











6.00 



6.00 



7.00 



6.50 



7.00 







N/10 KCl 







N/20 KCl 







N/30 KCl 







N/50 KCl 



2.00 



N/200 KCl 



7.00 



Distilled water 



6 00 







Full nutrient solution as 

 the solvent 

 N/4 KCl 







2.50 

 5.00 

 6.25 



7.50 

 6.25 





 Slight 

 3.75 

 7.50 



10.00 

 8.75 



2.50 

 5.00 

 6.25 

 7.50 



8.75 

 7.50 







N/5 KCl 



N/7 KCl 



1 . 50 No branches 

 6 . 25 Few branches 



N/10 KCl 



7 . 50 Slightly 



N/50 KCl 



branched 

 11.25 



Nutrient solution 



10.00 Branched 



Toxicity of sodium 

 Sodium ions in distilled water are somewhat more deleterious to pea 

 and wheat seedlings than are potassium ions. No top growth results in 



