igig] 



ROSE— BLISTER CANKER 



135 



in the series. Its catalase activity is less than that of either of the 

 others and seems to be less affected by tissue acids when no car- 

 bonate is added. It is possible that near the canker the host's 

 catalase is injured by materials from the fungus, even in advance 

 of actual invasion by the hyphae. The fungus catalase may not 

 appear here at all, but only later in the diseased bark, and in 

 increasing amounts as the amount of mycelium increases. 



The oxidase activity of samples 13, 15, 17, 19, together with the 

 catalase activity of samples 14, 16, 18, 20, identical with them 

 except for the addition of carbonate, are given in table XXI. 



TABLE XXI 

 Catalase activiiy of apple bark 



Description of sample 



Healthy 



Healthy ( ?) 5 cm. from canker 



Diseased 



Dead 



Manometer readings expressed 



IN CM. OF mercury USING O.I 

 CM. OF BARK POWDER 



Catalase 



Oxidase 



1. 16 

 1-47 

 1-95 

 0.88 



It will be seen that there is a gradual increase in oxidase activ- 

 ity from healthy to diseased bark, but a marked decrease in the 

 case of dead bark. The catalase is considerably lower in apparently 

 healthy bark near a canker than in the bark of an unaffected limb, 

 but very much higher in the bark killed by the fungus than in 

 bark from a healthy Umb. 



Microchemical analysis 



Tests for oxidase, peroxidase, and catalase were made on fresh 

 bark, all others on bark preserved in 50 per cent alcohol. The 

 results are given in table XXII. 



In making the tests for oxidase (direct action) and peroxidase 

 (indirect action), the brownish purple color due to oxidation of 

 benzidine was found most marked at first, in both healthy and 

 diseased bark, in a zone 2 or 3 cells wide just inside the cork and 

 in the pith rays. Later it came to about the same intensity over 



