158 University of California Publications in Agricultural Sciences [Vol.3 



liura chloride and calcium chloride. There is very little, if any, be- 

 tween ferric chloride and calcium chloride. Magnesium chloride and 

 ferric chloride show marked antagonism in all concentrations used 

 as do magnesium chloride and aluminum chloride in certain concen- 

 trations of the two salts. Magnesium chloride and ferric chloride 

 show marked antagonism in all concentrations as do magnesium 

 chloride and aluminum chloride in one concentration of the latter salt. 



Reference has already been made to Miss Brenchley's monograph 41 

 and to the paper by Lipman and Gericke, 42 in which the literature 

 relating to the effects of copper, zinc, and iron salts on plants is 

 reviewed. Suffice it to say that the results reported by different 

 investigators are very conflicting, due largely to the widely different 

 methods used and the varying conditions under which the various 

 data were obtained. 



In the present work, copper chloride was toxic in every concen- 

 tration used. There was marked antagonism between copper and 

 ferric chlorides both from the standpoint of growth and of absorption. 



Copper sulphate did not prove to be uniformly toxic. Growth was 

 nearly normal in one concentration used while very much diminished 

 in a lower concentration. The term stimulation might be applied 

 here, but in the present discussion it is applied only when growth due 

 to the presence of an added salt or salts is undoubtedly greater than 

 that in the control. 



Toxic effects are correlated with increased absorption and antag- 

 onistic effects with decreased absorption as in other series reported. 



Growth was always less with zinc sulphate present in the nutrient 

 solution than in the latter alone. Copper and zinc sulphate together 

 were no more toxic than a solution of zinc sulphate alone. 



The case with ferric sulphate is clearly one of stimulation. The 

 dry weight was over twice that of the controls in one concentration 

 of the salt used and far superior in several concentrations to that 

 of the plants grown in the controls. Wolff 43 has reported similar 

 results when iron was used in the form of the citrate, an increase 

 in growth comparable to that noted above having been obtained. He 

 found further that nickel or chromium could not be used to replace 

 iron. 



The toxic effects of copper sulphate were markedly reduced by 

 the presence of ferric sulphate when we consider the results as a 



4i Inorganic plant poisons and stimulants. 1915. 

 42 Univ. Cal. Pub. Agr. Sci., vol. 1 (1917), p. 395. 

 43C.-K. Acad. Sci. (Paris), vol. 157 (1913), p. 1022. 



