59 2 
Journal of Agricultural Research 
Vol. XXI, No. 8 
cent, and in most cases is much less. The data therefore show con¬ 
clusively that a strong positive correlation exists between catalase 
activity and growth even though the increased acidity of the medium 
would tend to increase the rate of destruction of catalase. 
From the several studies here summarized, in which decreased acidity 
has been shown to be correlated with production of overgrowths and 
high catalase activity in two instances 1 and increased acidity with over¬ 
growth production in the present case, it must be concluded that such 
changes in acidity have little to do with catalase or overgrowth, unless 
it should be found that increasing or decreasing the acidity toward a 
certain value lying about P I£ 6.00 favors growth in the tissue affected. 
Acidity changes overlapping this value have not yet been found, but in 
the three cases investigated changes of reaction toward this value have 
been associated with overgrowth production. Further data are needed 
for deciding this point. It is remarkable how close the value for wart 
tissue lies to P H 6.00. It varies not more than 0.1 P„ from this value, 
although tlie acidities of different potato varieties vary as much as 0.5 
P H from each other. 
It is evident from Table I that differences in the acidity of the potato 
varieties are not associated with resistance to the disease as shown by the 
production of overgrowths. 
SUMMARY 
A study was made of hydrogen-ion concentration and catalase activity 
in a new type of plant overgrowth, the wart disease of the Irish potato 
caused by Chrysophlyctis endobiotica. 
The hydrogen-ion concentration of wart tissue is constantly greater 
than that of healthy tubers from the same plant, the values being repre¬ 
sented by P H 6.00 and P n 6.49, respectively. 
Catalase activity is much greater in the wart tissue, the values being 
represented by 17.9 cc. of 0 2 for diseased and 7.8 cc. for healthy tissue! 
Catalase activity is strongly correlated with growth in spite of the 
higher acidity of the proliferation. This differs from other types of plant 
overgrowths previously studied in which diminished acidity is correlated 
with increased catalase and growth activity. 
Differences in acidity of the varieties are not associated with immunity 
to the disease. 
1 Harvey, R. B. relation or cataease, oxidase and h+ concentration to the formation of 
overgrowths. In Amer. Jour. Bot., v. 7, no. 5, p. 211-213. 1920. 
hardening process in plants and developments from frost injury In Jour Agr 
search, v. 15. no. 2, p. 83-1.2, 3 fit'., pi. 7-1 1 and A (col.). i 9 rS. Literature cited, p. icS-irr. ' " . 
