THE EFFECTS OF CONDITIONS OF GROWTH UPON 

 SUSCEPTIBILITY TO FUNGOUS DISEASES. 



By Prof. B. M. Duggar, Ithaca, New York. 



Delivered before the Society, January 30, 1909. 



The John Lewis Russell Lecture. 



In the Proceedings of this Society, I notice that the fungous dis- 

 eases of horticukural plants have been given Uberal consideration. 

 The papers on this topic in 1898 and 1899 presented most interest- 

 ing facts of general significance with respect to host resistance and 

 the phenomenon of disease. In 1905 an historical sketch of the 

 work accomplished was recorded. Other reports have included dis- • 

 cussions of most of those special diseases which are of peculiar im- 

 portance to the floricultural and fruit cultural interests. It has, 

 therefore, seemed appropriate to occupy this hour with the question 

 of how certain conditions of growth, or factors of the environment, 

 may play a part in the relations of host to parasite. This seems to 

 be a phase of the general subject of fungous diseases which has 

 received less than a proportionate share of attention, and it is one of 

 growing experimental importance. When the duty of the plant 

 pathologist seems to have been accomplished in the matter of dis- 

 covering new diseases or working out life histories, there will still 

 remain a field of valuable research in which the relation of the host 

 and parasite are the chief problems. 



It is not to be understood that the problem of working out the 

 causes of new or obscure diseases is growing less important. On 

 the contrary a review of the work of the past year in this country 

 alone would bring out creditable additions to our knowledge of com- 

 mon diseases, and some new diseases of peculiar interest. I recall 

 that at last the precise nature of the wonderfully destructive crown 



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