THE PERMEABILITY OF CELLS 535 



control. Chloroform water induces the formation of an acid in 

 the vacuole and the production of acid in solution of weak alkalies 

 is probably one factor in the return of the red color. 



Failure of Elodea leaves to become red when once turned yellow 

 by KOH is not due to the longer time required by the KOH to 

 bring about the color change (the neutral red diffusing out slowly 

 in the interval), because the leaves become yellow within one 

 minute, if placed in t^ KOH yet in pure water the red does not 

 return. 



We must seek an explanation of the reversibility of the NH4OH 

 change, the irreversibility of the KOH change in the different 

 degrees of hydrolytic splitting of the respective NH4 and K salts 

 of the acid with which the neutral red combines. If R is the acid 

 radical within the plant and D the neutral red radicle, the reactions 

 may be represented thus: 



RCOOH + DOH = RCOOD + H2O. 



RCOOD + NaOH = RCOONa + DOH 



RCOOD + NH4OH = RCOONH4 + DOH 



The RCOONH4 salt of a weak base and a weak acid undergoes 

 a greater hydrolytic sphtting than the RCOONa combination, the 

 NH4OH formed diffuses rapidly away and recombination of 

 RCOOH and DOH again take place. 



The difference in resistance of the plasma membrane to NH4OH 

 and NaOH is strikingly shown in the following experiment. If 

 we remove Elodea leaves, after decolorization in NH4OH to 

 chloroform water (one minute) and then place them in 5^ NaOH 

 there is never a return of the red color. Chloroform destroys the 

 plasma membrane and the KOH may penetrate rapidly. On 

 the other hand, if the leaf decolorized in to NH4OH is placed in 

 /o NaOH, without previous chloroform treatment, its cells become 

 red again just as they would in pure water. The conditions for 

 demonstrating any entrance of NaOH are here most favorable, 

 the neutral red is already in the alkaline condition, the proteids 

 have taken up the amount of NH4OH necessary before and alka- 

 line reaction may be indicated, yet the NH4OH diffuses rapidly 



