Relation to Deleterious Chemical Agents 443 



plants. Some of the results secured by Kahlenberg and 

 True are given in the table below, where also a compari- 

 son may be made with acetic acid, the latter occupying 

 an intermediate position with respect to toxicity among 

 organic acids : 





In these experiments the roots of a few seedlings were 

 immersed in 300 cc. of solution (the acid in distilled water) 

 and the concentrations given are just sufficient to kill at 

 least 50 per cent of the roots after an exposure of 24 hours. 

 The toxicity of inorganic acids is strikingly reduced by the 

 presence in the solution of solid particles. 



268. Alkalies. Alkalies are in general less toxic to the 

 roots of seed plants than are equivalent concentrations of 

 acids or of salts of the heavy metals. In order to inhibit 

 root growth of seedlings in water cultures, it requires from 

 5 to 10 times as strong a solution of caustic alkali as of a 

 mineral acid. Alkalinity (basicity) and acidity as applied 

 to field conditions are merely relative terms, since under 

 such conditions the usual methods of determining these 

 qualities are inaccurate. It is well known, however, as in- 



1 Approximate. 



