Walter Stiles 
138 
condition. In this way the critical concentration of a number of 
acids, that is, the concentration necessary to injure the cells in a 
certain time, was found for different plant cells. The critical con¬ 
centration of hydrochloric acid, for example, in the case of hypodermal 
cells of red cabbage immersed for four hours in the sucrose solution 
containing the acid, was N/yoo, corresponding to a hydrogen-ion 
concentration of 1*4 x io~ 3 . 
In his experiments on antagonism a similar procedure was 
employed, the hydrochloric acid in various concentrations being 
added to a number of salts in solutions which gave approximately 
equal plasmolysis. The sections were placed for 20 minutes in these 
plasmolysing solutions, then for four hours in the solution of salt 
+ acid. They were then transferred successively into a half-strength 
salt solution, a quarter-strength salt solution and distilled water. 
The concentrations of salt used, the concentration of hydrochloric 
acid in the salt solution, and the actual hydrogen-ion concentration, 
determined by the hydrogen electrode, of the mixed solution, are 
shown in Table XLV. 
Table XLV 
Critical Concentration of hydrochloric acid in regard to hypodermal 
cells of red cabbage in presence of various salts and sugars. 
(Data from Brenner) 
Salt or sugar 
Concentration 
of salt or sugar 
in per cent. 
Critical 
concentration of 
hydrochloric acid 
Actual hydrogen-ion 
concentration of 
the solution 
Sodium chloride 
2-2 
I X IO -3 
8-91 X IO -4 
Potassium nitrate 
375 
1-25 X XO -3 
1-29 X IO” 3 
,, chloride 
2*8 
1-67 X IO -3 
1-38 X IO” 3 
,, sulphate 
Magnesium nitrate 
5 -o 
2*5 X IO -3 
4-68 x io~ 4 
8-8 
I X IO -3 
1-09 X IO -3 
,, chloride 
yo 
2-5 X IO” 3 
3-16 X IO -3 
,, sulphate 
16a 
4 X IO -3 
1*12 X IO” 3 
Calcium nitrate 
6*5 
2 X IO -3 
1*95 x io -3 
,, chloride 
6*2 
4 X IO“ 3 
5-50 X IO“ 3 
Glucose 
— 
1*43 x io” 3 
8*90 X IO - 4 
Sucrose 
20 
1-43 X IO -3 
8-71 X IO” 4 
It will be observed from the data presented in this table that the 
different substances examined affect very differently the resistance 
of the cells to hydrochloric acid. Sodium chloride has the same effect 
as sugar, while potassium sulphate lessens the resistance of the cells 
to about half. All the other salts, on the other hand, raise considerably 
the resistance of the cells to acids, as a much higher hydrogen ion 
concentration is necessary to injure the cells in the presence of the 
salts. 
