164 M. M. McCooL 



has made some experiments which show that the permeabihty of the 

 cell is altered, the data of which are reserved for future consideration. 



SUMMARY 



The results of extensive studies of the toxic and the antidotal action 

 of various ions have been presented. A general summary of these results 

 appears below: 



Pure solutions of N/500 MgClo or MgS04 prevent further elongation 

 of roots of seedlings. The toxicity of this cation is prevented by calcium 

 in cultures composed of N/20 CaCl2 with N/20 or any greater dilution of 

 MgCls; and N/1000 CaClo is effective with N/200 MgCls, but not with 

 N/20 MgCl2. N/50 MgCl2 or higher concentrations are toxic in a dilute 

 full nutrient solution. The further addition of CaCl2 counteracts this 

 injurious action. 



Mutual antagonism exists for wheat seedlings when N/50 KCl is present 

 in solution with N/100 to N/1000 MgCl2. N/1000 KCl likewise 

 counteracts the toxicity of N/500 MgCl2. 



The sodium and magnesium relations are similar to those of potassium 

 and magnesium; however, sodium is not so effective as potassium in 

 antidoting the magnesium ion. 



No elongation of roots of pea seedlings takes place in N/20 KCl; but 

 the presence of CaCl2 at a concentration of N/20 to N/500 completely 

 counteracts this deleterious action. 



Very dilute solutions of calcium are effective in overcoming the poison- 

 ous action of sodium. N/5000 CaCl2, for example, prevents injury by 

 N/50 NaCl, and this ratio is almost as effective as when N/20 CaCl2 is 

 used with N/50 NaCl. 



N/4000 NH4CI is toxic to pea and wheat seedlings, the elongation of 

 roots being less than in distilled water. The presence of N/5000 CaCl2 

 in solution with N/1000 NH4CI greatly lowers the harmful action of 

 ammonium ions. No injury results to pea seedlings placed in cultures 

 composed of N/20 CaCl2 + N/100 NH4CI. 



Salts of ammonium in a full nutrient solution are far less toxic than in 

 distilled water. N/100 NH4CI is only slightly injurious with the nutrient 

 solution employed, but with N/25 death of seedlings soon results. The 

 further addition of CaCl2 so that its concentration becomes N/25 or 

 N/100 entirely counteracts the toxicity in the one case and decreases 

 the injury in the other. 



