114 



BOTANICAL GAZETTE 



[FEBRUARY 



It is clear from table V that oxidation in these mixtures is 

 accompanied by a marked increase in hydrogen ion concentration, 

 and the conclusion certainly seems justified that there is a causal 

 relation between the two. It is also seen that when oxidation 

 comes to an end, both mixtures have the same reaction, Ph = 4 • 29, 

 a condition suggesting that at this point the hydrogen ion is the 

 limiting factor. 



BuNZELL (12) and Reed (28) have studied the effect of hydrogen 

 ion concentration on oxidation, but apparently neither of them has 

 realized that it might increase during the oxidation process (30). 

 They apparently assume that the hydrogen ion concentration 

 established at the beginning of an experiment remains constant 

 until the end, whereas the results given show that in these cases 

 it increased as long as the oxidation continued. 



In order to discover, if possible, what relation exists between 



oxidation and hydrogen ion concentration in the oxidase apparatus, 



further experiments were tried with mixtures of bark, dry pyro- 



gallol, and, instead of water, 5 cc. of buffer solutions containing 



various amounts of N/io sodium acetate and either N/io or 



N/ioo acetic acid. The initial reactions of these mixtures (before 



shaking) and of the buffers alone are given in table VI and shown 



graphically in fig. 2. 



^ ^ ^ TABLE VI 



Reaction, Ph, of buffer solutions and mixtures of buffer solutions, 



bark, and pyrogallol 



Graphs B and C in fig. 2 show that while diseased bark absorbs 

 H+ ions to about the same extent as the healthy, the latter absorbs 

 more 0H~ ions; that is, its titration acidity is greater, which 

 is exactly the condition found by titration with N/20 sodium 

 hydroxide (30). The Ph values at points where B and C cross A 



