I9I9] 



ROSE— BLISTER CANKER 



113 



different treatments as shown. The results show that oxidase 

 activity is much reduced by drying at 35-40° for 4 hours (sample i, 

 healthy; sample 2, diseased), or at 50° for 2 hours (sample 5a, 

 healthy). 



Hydrogen ion concentration.— Hydrogen ion determinations 

 on mixtures of bark and water and of bark, water, and pyrogallol, 

 used in the same proportions as in the oxidase apparatus, showed 

 that pyrogallol has no effect on the reaction. It was found pos- 

 sible to get constant initial readings on all mixtures containing 

 healtTiy bark and pyrogallol in 30-45 minutes; the same period 

 sufficed for mixtures containing diseased bark and pyrogallol after 

 they had been shaken in the oxidase apparatus, but not for similar 

 mixtures freshly made up and not shaken. In these cases the 

 potential increased slowly for an hour or two from about Ph = 5 . 60 

 to Ph = 5.40, but never reached the figure given by healthy bark. 



Culpepper, Foster, and Caldwell (16), working with normal 

 and diseased Red Astrachan apples, state that when titrations were 

 made on fruit pulp suspended in water " the diffusion of acids out 

 of the tissues continues for many hours and at slower rates in 

 diseased than in normal fruits," but in the light of the following 

 results the writer is inclined to think this increase of acidity was 

 due to oxidation going on in the solutions, and not to diffusion of 

 acids out from the tissues. 



TABLE V 



Correlation between oxidase activity and htorogen ion concentration 



OF MIXTURES CONTAINING PYROGALLOL, WATER, AND EITHER HEALTHY 

 OR DISEASED BARK; TEMPERATURE 29-30.5° C. 



Increase in hydrogen ion concentration during oxida- 

 tion. — Experiments designed to test more fully the theory that 

 oxidation causes an increase in acidity are summarized in table V. 



