o 



02 BOTANICAL GAZETTE [april 



and variation of this organism, which causes potato scab, and 

 concerning which we cannot decide as yet whether it belongs to 

 the Eumycetes or to the bacteria. 



Morbid histology of the various diseases presents a large field 

 for activity. Concerning many diseases our knowledge in 

 regard is as yet really nil. It may be in many cases that 



this 



has done so. Its 

 tree surgery, etc. 



many 



smuts 



The whole question of disease-resistance and susceptibility is 



fundamental and 



the 



mechanical 



the factors of air, soil, or heredity causing variation in resistance, 

 and the possibility of artificially changing these factors. Breeding 



em 



mg 



the needs of cultural conditions, and laws of breeding. Notable 

 progress has been made with many crop plants, as oats, cabbage, 



melon 



some 



t of much study. 

 It is, of course, 



in many cases with 



seems also sadly in need of study by those with sound ecological 

 training. Indeed, an ecological study of certain plant parasites, 

 with analysis of the environmental factors and with environments 

 under experimental control, touching also upon seasonal relations, 

 should be very productive. Problems abound on the border 

 fields between mycology, physiology, ecology, and pathology 

 relating to the age relation to disease, to mode of infection, to the 

 climatic and seasonal relations of the parasite, to increase and 

 decrease of susceptibility with, changes of environment, to the 

 results of varying the mass of the inoculum, and to change of the 

 virulence of the pathogen with environment. 



Epidemiology (to borrow the term from medical usage) is 

 clearly linked with these topics. There is a vast amount of uncor- 

 related information in the literature concerning the relation between 



temperature, rainfall, etc., and various diseases, but there is ample 



