THE PERMEABILITY OF PROTOPLASM 



121 



that of the solution of B, a better growth may in some 

 cases occur in the former. To compensate for this the 

 concentration of A must be slightly increased, in order to 

 obtain truly isotoxic solutions. When the effects of the 

 two salts used are additive, a straight line parallel to the 

 concentration axis represents their action, as in Fig. 7. 



FIG. 7. CURVES SHOWING THE GROWTH OF ROOTS IN MIXTURES OF 

 EQUALLY Toxic SOLUTIONS OF Two SALTS, A AND B. 



The ordinates represent growth and the abscissae represent the compo- 

 sition of the mixture in molecular percentages. 



The antagonism of any mixture may then be expressed 

 as the height of the curve, at any concentration, which 

 rises above this straight line, divided by the distance of 



TC T 



the straight line from the base. Thus, in Fig. 7, - rep- 



J JDJ 



resents the antagonism of an equimolecular mixture of 

 A and B. This may be expressed conveniently as a per- 



