214 
R. B. HARVEY 
the total concentration of the expressed juice must be the same as that 
within the tissue to obtain a true value ; for the H+ concentration this is not 
necessarily the case. 
Although the differences in H+ concentration shown in the above table 
are small, they may be of relatively great importance for the activity of 
the respiratory enzymes associated with growth. The curve for the 
activity of catalase of plant origin at various H+ concentrations is prac- 
tically the same as that for catalase of animal origin given by Michaelis 
(8). From this curve it will be seen that the H+ concentration shown by 
the plant tissue lies in a critical region for the activity of catalase. A 
change from Ph 5.52, the average value for healthy stem tissue of Ricinus, 
to Ph 5.78, the average value for tumor tissue, increases the catalase 
activity 25 percent at an acetate concentration of fiftieth normal. The 
activity of oxidase is increased also by a decrease in the H+ concentration. 
In a paper cited above (7, pp. 98-101) the author gave indications of the 
decrease in H+ concentration resulting from freezing of leaf tissue. Areas 
of Bryophyllum leaves which contain anthocyanin are changed from red 
to blue on freezing. This is not necessarily accompanied by death of the 
tissue. 
It is shown from the work by Dr. Smith and others (9, p. 113) that 
Bacterium tumefaciens blues litmus milk and decreases the H+ concentration 
of the culture medium. This it appears to do also in the tissue in which 
it grows. 
Since catalase is destroyed at increasing rates with increase in the hydro- 
gen-ion concentration, it is of interest to compare the catalase activity of 
two tissues of the same plant which were the same before overgrowth was 
induced by stimulation but which finally have different hydrogen-ion con- 
centrations. For this purpose, Ricinus plants were inoculated with B. 
tumefaciens and when the tumors had become sufffciently large they were 
removed. Healthy stem tissue was taken from the same node. Fifty 
grams of tissue were ground in a mortar with crushed quartz and 25 cc. 
of phosphate buffer mixture Ch 2.7 X io~^, and made up to 500 cc. with 
distilled water. The Van Slyke apparatus for amino-acid determination 
was found convenient for catalase determination when used in a constant 
temperature room. Five cc. of hydrogen peroxide (Oakland 3 percent 
neutral*) was run into the reaction chamber of the apparatus and washed 
down with 10 cc. of distilled water. After adjusting the level in the measur- 
ing pipette, 10 cc. of plant tissue dilution was run in from the side burette. 
The apparatus was shaken only fast enough to give a good mixing of the 
solution, and the rate of shaking was kept the same throughout. After 
10 minutes the following amounts of oxygen were evolved at 30° C. 
Tumor tissue 44.6 cc. O2 42.3 cc. O2 
Healthy stem tissue 13.2 cc. O2 13.3 cc. O2 
Bryophyllum leaves were inoculated with B. tumefaciens by injecting a 
