590 
Journal of Agricultural Research 
Vol. XXI, No. 8 
frequently equaling or even exceeding the normal size of the organ 
which they replace, and they develop very rapidly—much more so 
than bacterial tumors. For instance, the earliest wart infections at 
Freeland, Pa., this year were found about July 13, and they were then 
not larger than 1 to 2 cm. in diameter. By the last of July warts 5 cm. 
or more in diameter were abundant, and some could be found even as 
much as 10 cm. in diameter and weighing 200 gm. Evidently growth is 
exceedingly rapid in the infected tissues, and this disease affords excellent 
material for a separation of the physiological factors affecting growth. 
The hydrogen-ion determinations were made by the potentioinetric 
method, using a bubbling electrode. The tests were run in pairs with 
wart and healthy tuber tissue collected from the same plant while in 
full vegetative activity and taken directly to the laboratory for testing. 
The material was ground in a food chopper and the juice pressed out 
through a cloth sack. No effort was made to use always uniform pressure 
with the different samples, because the hydrogen-ion concentration of an 
expressed juice depends not upon the total concentration of buffer 
substances present but upon the ratio of their concentrations. The 
samples were tested without dilution. It was observed that oxidase 
activity was much greater in wart tissue, judging by the very dark color 
which the expressed juice acquired as compared with the light color of 
healthy juice. 
Table I.— Hydrogen-ion concentration in healthy and wart tissue from the same plant 
Variety. 
Healthy. 
Wart. 
Ph. 
Ch+. 
Ph. 
Ch+. 
Prince Henry. 
6. 17 
6. 7 X10- 7 
5 - 96 
M 
s 
X 
l 
Ehnola. 
6.36 
4.3 Xio- 7 
Immune. 
Immune. 
Irish Cobbler. 
6.49 
3.2 Xio- 7 
Immune. 
Immune. 
Rural New Yorker. 
6.45 
3. 5 Xio- 7 
6. 11 
7. 76Xio- 7 
Do. 
6-39 
4. 07Xio- 7 
6. 05 
8. 99Xio- 7 
Up-to-Date. 
6-35 
4. 47Xio- 7 
5 - 99 
1. 02 X io-° 
Edzell Blue. 
6. 50 
3.16X10- 7 
Immune. 
Immune. 
Seedling 39168. 
6. 67 
2. 14 Xio- 7 
Immune. 
Immune. 
Seedling 38816. 
6. 65 
2. 24Xio- 7 
6. 09 
8. 13 Xio- 7 
McCormick. 
6. 49 
3. 24Xio- 7 
Immune. 
Immune. 
Carman. 
6 - 57 
2. 69Xio- 7 
6. 01 
9. 77Xio- 7 
Rose No. 4. 
6. 48 
3. 31 Xio- 7 
Immune. 
Immune. 
Portuguese Purple. 
6. 65 
2. 34Xio- 7 
5. 90 
1. 26X10- 6 
Early Prospect. 
6. 46 
3. 47 Xio- 7 
6. 03 
9 * 33Xio- 7 
Average. 
6. 49 
3. 48Xio- 7 
6. 00 
9. 71 Xio- 7 
The catalase determinations were made on diseased and healthy 
tissue from the same plant, using fresh material. The Van Slyke amino- 
nitrogen apparatus was used. 1 All determinations were made by using 
1 Harvey, R. B. relation or catalase, oxidase, and h+ concentration 
OF overgrowths. In Amer. Jour. Bot., v. 7, no. 5, p. 211-213. 1920. 
TO THE FORMATION 
