140 M. M. McCooL 



Fig. 3. — Antidotal relations between sodium and magnesium; distilled ivater as the solvent 



1. N/50 NaCl+N/100MgCl2 5. N/oONaCl 



2. N/50NaCl+N/500 MgCb 6. N/1000 NaCl 



3. N/50 NaCl +N/ 1000 MgCl2 7. N/500 MgCh 



4. N/1000 NaCl +N/500 MgCh 8. DistiUed water 



Calcium and potassium 



It has been shown by various investigators that salts of potassium are 

 commonly much less toxic than those of magnesium. Nevertheless, 

 a relatively weak concentration of KCl, N/50, will completely inhibit the 

 growth of roots of the field pea; and it is only when the concentration is 

 reduced to about N/500 that root groT\d:h is approximately equal to that 

 when the plant is in distilled water. It has already been shown that 

 calcium salts, at concentrations approaching the threshold of plasmolysis, 

 may show little or no inhibition as compared with distilled water. When 

 the salts of the two bases calcium and potassium are combined in certain 

 proportions the toxicity of the potassium is entirely overcome, and the 

 growth of the Canada field pea seedlings is considerably greater than in 

 the corresponding concentrations of the calcium salt employed alone. 

 This increase is of course partly due to the presence of another essential 

 element. In general, the writer's results confirm and extend those of 

 Kearney, Osterhout, Hansteen, and others, indicating that there is suf- 

 ficient evidence to interpret the relation between these bases as one 

 of mutual antagonism. Osterhout (1909), experimenting with wheat, has 

 shown this relation as affecting root gro'wth, and the following table in- 

 cludes some of the more significant of his results: 



