1919] ROSE— BLISTER CANKER 143 



2. The gradual slowing down of oxidation in the Bunzell 

 apparatus is shown to be due, in part at least, to increasing hydrogen 

 ion concentration, brought about by the oxidation process itself. 

 The equilibrium reached in the oxidase apparatus seems to be a 

 false one, which can be disturbed by the addition of either fresh 

 oxidase reagent or plant material. When tested by the formula 

 for a unimolecular reaction, the oxidase reaction gives values for 

 k, which indicate clearly a linear relationship between time and 

 amount of change and suggest that the oxidase is a catalytic agent, 



3. The hydrogen ion concentration of diseased bark (Ph = 5 -61) 

 is definitely less than that of healthy bark (Ph = 5.i5). Work 

 with buffer solutions shows that this difference is not great enough 

 to account for all of the difference in the oxidase activity of the 

 two kinds of material. When mixtures of the two are brought to 

 the same hydrogen ion concentration by means of buffer solutions, 

 diseased bark still shows greater oxidase activity. 



4. The temperature and duration of drying have an effect on 

 the acidity and the oxidase activity of both healthy and diseased 

 bark. 



5. Eight-tenths per cent gelatine increases the oxidase activity 

 of both kinds of bark. This may be due to the action of gelatine 

 as a protective colloid which prevents precipitation of the "oxidase." 

 It is not due to buffer action. 



6. The concentration of hydrogen ion necessary or complete 

 inhibition of oxidase activity of healthy bark lies between 3 .55 and 

 3 .8oXio~'*;for that of diseased bark between 3 .55 and4.27Xio~'^. 



7. Oxidation in the apparatus comes to an end only after several 

 days instead of after a few hours, as stated by Bunzell. 



8. When the "oxidase" is precipitated in 2 fractions, the first 

 has greater oxidizing power than the second, and the 2 combined 

 have slightly greater oxidizing power than when tested separately. 



9. Catalase determinations gave the following results: healthy 

 3.02 (cm, positive pressure), seemingly healthy 5cm. from the 

 canker i.oi, diseased 2.74, dead 12.17; results from oxidase 

 determinations for the same stages were 1.16, 1.47, 1.95, 1.85 

 (cm. negative pressure). These results show some discrepancies, 

 but justify the general statement that the more severely the bark 



