120 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



affords closely the same conductivity as the sap itself. 

 Table XXX, substantiates this selective permeability of 

 the protoplasm. In it A denotes the depression of freezing- 

 point, and C the electrical conductivity in mhos at 0, and 

 a few typical results are shown. It should be mentioned 

 that the pressed sap upon which these measurements 

 were made by Dixon and Atkins was freed from cell debris, 

 by means of a powerful centrifuge. 



THE MEASUREMENT OF THE ANTAGONISM OF IONS. 



Osterhout (1914, 1) has quite recently still further in- 

 creased the precision of investigations on the antagonism 

 of ions by introducing suitable quantitative criteria. As 

 a basis he advocates the mixing of equally toxic solutions. 

 This may give rise to one of three possible effects : 



1. The toxicity is unaltered, which means that the toxic 

 action of the two salts is additive. 



2. The toxicity is diminished, in which case the salts are 

 said to have an antagonistic action. 



3. The toxicity is increased. 



To represent these actions the molecular compositions 

 of the mixtures of equally toxic solutions of two salts, A and 

 B, may be taken as abscissae, and the amounts of growth 

 in any solution marked off as ordinates. Then in the 

 graph (Fig. 7) the additive effect will be represented by 

 the line LJM parallel to the composition axis; LKM is the 

 antagonism curve, and LHM shows the behaviour of 

 mixtures of increased toxicity. 



By the method of mixing two equally toxic solutions 

 disturbances due to variations in osmotic pressure are 

 eliminated. For if one substance, A, is twice as toxic as 

 another, B, mqlecule for molecule, it is evident that a 

 solution of A M / 20 will be isotoxic with a solution of B M / 10 . 

 But if the osmotic pressure of the solution of A is less than 



