160 



M. M. McCooL 



Calcium and barium 



Additional antidotal relations of calcium and barium with respect to 

 pea seedlings are summarized in the following table: 



TABLE 28. Experiment with Canada Field Pea. Duration, Thirty Days. Data 



FOR Ten Plants 



Composition of solution 



N/10 CaCL+N/100 BaCk. 

 N/10 CaCl2+N/500 BaCl2.. 

 N/10 CaC]2+N/l,000BaCl: 

 N/500 BaCU 



N/1,000 BaCh 



Distilled water 



Green 

 weight 

 of tops 



(grams) 



5.20 

 5.80 

 7.40 

 Dead 



4.20 

 5.30 



Green 

 weight 

 of roots 

 (grams) 



4.20 



4.70 



5.20 



Slight 



2.85 

 3.45 



Total 



green 



weight 



(grams) 



9.40 

 10.50 

 12.60 



7.05 



8.75 



Average 

 length 

 of tops 

 (centi- 

 meters) 



13.0 

 11.0 

 13.0 

 Very slight 

 growth 

 17.0 

 10.0 



Average 

 length 



of roots 

 (centi- 

 meters) 



8.0 

 9.0 

 8.5 

 Very slight 

 growth 

 7.0 

 6.0 



A comparison of the data presented in tables 17 and 28 reveals the fact 

 that older seedlings are far more resistant to barium ions. It may be 

 cited, for example, that N/4000 BaClo prevents further elongation of the 

 roots of young seedlings, whereas N/500 is required to kill older seedlmgs. 

 The greater resistance may be due to mass relations; that is, the salts taken 

 up from the nutrient solution may prevent the entrance of barium ions 

 from the weaker solutions. Again, the more nearly complete migration 

 of the storage products from the seed to the root may react in like manner. 

 Furthermore, the permeability of the cell membrane may be altered and 

 thus the entrance of the toxic ions may be retarded. The first postula- 

 tion is unlikely, as the writer has found from several sets of experiments 

 that seedlings which have been grown for ten days in distilled water are 

 apparently no more susceptible to toxic ions than are those grown for 

 the same length of time in full nutrient solution. 



Stronger solutions of barium are required to exert toxic action toward 

 older seedlings; but in this case also calcium is effective in preventing the 



