Effect of Arsenic Compounds 



55 



With sodium arsenite the dilutions were carried further, to 

 1/250,000,000, but this still depressed barley to some extent (Fig. 13). 



Shoot 



Roor 



Fig. 10. Curve showing the mean value of the dry weights of ten series of barley plants 

 grown in the presence of arsenious acid and nutrient salts. (March 16th May 9th, 

 1911.) 



9<. 



Fig. 11. Curve showing the mean value of the dry weights of ten series of pea plants 

 grown in the presence of arsenious acid and nutrient salts. (June 8th July 21st, 

 1910.) 



With peas the results vary somewhat in the different tests, the depres- 

 sion with 1/2,500,000 and less being usually slight, though occasionally 

 it is much more strongly marked (Fig. 14). In a single series with 

 sodium arsenate barley was apparently unaffected by a concentration 



