78 MASSACHUSETTS HORTICULTURAL SOCIETY 



vironmental conditions, in order to be susceptible respectively 

 to the attacks of the asparagus rust, the American gooseberry 

 mildew, the grape mildew, and the potato blight. There is enough 

 difference in the normal climate of eastern North America and 

 Europe to warrant marked changes in the behavior of any intro- 

 duced organisms. Many vigorous European species of trees, 

 for example, are a failure when introduced into the eastern United 

 States, and have been for years. 



The main fact in support of a foreign origin of the disease is 

 its unquestionable spread in all directions from the vicinity of 

 New York City. It is further suggestive that the oldest centers 

 of infection located outside of the vicinity of New York City — 

 Bedford County, Va., and Baltimore Co., Md. — contained chest- 

 nut orchards with Japanese chestnut trees, possibly also European 

 varieties. If Diaporthe parasitica is a native fungus, or has 

 evolved from a native saprophyte, it is necessary to assume that 

 the saprophyte was very limited in range, or that the evolution to 

 a condition of parasitism occurred in only one, or at most a very 

 few localities, or that there is a chronological sequence in its 

 evolution proportional to its distance from New York City. Any 

 of these assumptions are a severe tax on the scientific imagination. 



There are moreover striking indications that, as it spreads, 

 the parasite is varying both morphologically and in its mamier of 

 working. The great divergence of views regarding many phases of 

 the disease is largely due to the fact that different investigators 

 are working under different conditions and in different localities. 

 It is quite impossible from observations confined to one county 

 or State to draw conclusions regarding the behavior of the disease 

 over its entire range. There is hardly an observation to be made 

 regarding the disease in any one locality which is not contra- 

 dicted by observations in some other place. Now this variation 

 is exactly what would be expected of any organism rapidly spread- 

 ing into new territory. 



However, before final conclusions can be drawn, it will be 

 necessary to correctly name the fungus, and determine where, if 

 anywhere, it is to be found outside of North America. At present 

 it is not known to occur except in the United States, and does not 

 appear to have been collected here prior to 1904. 



