\OLUiME LXVII NUMBER a 



THE 



Botanical Gazette 



FEBRUARY igig 



BLISTER CANKER OF APPLE TREES; A PHYSIOLOGI- 

 CAL AND CHEMICAL STUDY 



CONTRIBUTIONS FROM THE HULL BOTANICAL LAB0R.4T0RY 246 



Dean H. Rose 



(with ten figures) 

 Introduction 



It is now generally recognized that among the most important 

 problems of plant pathology are those coimected with the physiol- 

 ogy of diseases whose etiology is already known. It is also recog- 

 nized that this must be the physiology of the host, of the parasite, 

 and of the two in relation to each other, and, further, that such a 

 comprehensive view of all the factors involved furnishes the only 

 rational approach to an understanding of the principles underlying 

 immunity and disease resistance. 



In the present paper are given the results of a physiological 

 study of the destructive disease known as Illinois or blister canker, 

 the etiology of which, including the identity of the causal organism, 

 Nummular ia discreta (Schw.) Tul., was worked out by Hassel- 

 BRING (22) in 1902. The work reported here is a continuation of 

 an earlier investigation b}- the writer (30) on the oxidase activity 

 of healthy and diseased bark; in addition there is included an 

 account of the catalase activity and microchemical and macro- 

 chemical analyses of both kinds of tissues. Further work is planned 

 on the chemistry of the disease, on the role of other enzymes than 

 oxidases, and on the physiology of the fungus itself in pure culture. 



105 



