1918] Waynick: Antagonism and Cell Permeability 159 



whole, although in one instance growth was greater with copper sul- 

 phate alone than when both salts were added together. 



The second case of stimulation was noted with zinc sulphate and 

 ferric sulphate in certain concentrations. In series 26 four cultures 

 gave growth superior to that obtained in the control for the series, 

 and throughout growth was good when the two sails referred to above 

 were present together, over the range of concentrations employed. 

 Low absorption was noted. In summarizing the relations of ferric. 

 cupric and zinc sulphates, it is evident, from the discussion above, 

 that zinc sulphate was toxic in every concentration used. Copper sul- 

 phate was toxic, but marked variation in degree was shown between 

 various concentrations. Ferric sulphate was stimulating. Copper 

 sulphate and zinc sulphate were no more toxic, together than when 

 each was used alone. Ferric sulphate modified somewhat the toxic 

 effects of copper sulphate. Zinc sulphate and ferric sulphate together 

 proved stimulating to the growth of plants. As contrasted with the 

 chlorides, the sulphates of copper and iron were less toxic to barley 

 over the range of concentrations used in this investigation. 



Taking the results as a whole, twelve instances of a marked in- 

 crease in growth at certain definite concentrations of one or more 

 added salts have been noted. "With every such increase there is a very 

 notable decrease in the amount of calcium and magnesium absorbed. 

 The increase in growth is attributed to antagonistic salt action: de- 

 creased absorption is undoubtedly due to the same action, which 

 tends to preserve the normal permeability of the plasma membrane. 



In addition to the twelve instances referred to above, we find 

 in series after series, the toxic effects of the solution in which the 

 plants were growing, noticeable not alone by decreased growth but 

 also by increased absorption. The roots and tops may not show the 

 same relations as regards the amounts of calcium and magnesium 

 taken up. For example, in series 25, in which ferric sulphate and 

 mercuric chloride were used together, the toxicity of the solutions was 

 evident by the very limited growth, yet the composition of the top- 

 was about normal. Tn the roots, however, the percentage of mag- 

 nesium was found to be tremendously increased. 



It is of interest to refer again to the very low ash content and 

 relatively low absorption, considering the very limited growth, in the 

 few cultures in which mercuric chloride was used alone. It is pos- 

 sible that relatively large amounts of mercuric salts were taken up 

 by the plants which were volatilized on ashing the residue; thus the 

 low pen-* ntage of ash may be less surprising. 



