ENDOTHIA CANKER OF CHESTNUT 555 
(2) it was an introduced species. When a fungus produces a sudden and 
destructive epiphytotic the presumption is that it has been introduced 
from some foreign country — a presumption that is supported by numerous 
well-known analogous cases in the past. But, on an investigation of 
conditions in other countries, no record of a similar disease of the chestnut 
could be found. This, however, does not invalidate the importation 
theory, since it is a fact well-known to plant pathologists that a fungus 
may be an inconspicuous and comparatively harmless parasite in its 
native country and yet may produce a destructive epiphytotic on being 
taken to another country. 
This theory was first advanced by Metcalf (1908a). Since he was 
unable to find any record of the occurrence of the disease in this country, 
and since he found the Japanese chestnuts more or less immune, he 
suggested that the fungus was a native of Japan and had been introduced 
here on imported trees. The presumption would be that, spreading to 
our native chestnuts, the fungus found these less resistant and more 
favorable to its growth; hence its rapid spread throughout the eastern 
States. In February, 1912, just previous to the Harrisburg Conference, 
Metcalf (1912 b:77-78) discussed his theory in part as follows: 
“My own working hypothesis is, that the parasite is an importation 
from some country other than North America. The resistance of the 
Japanese and Korean chestnuts, coupled with the fact that the Japanese 
chestnut has been extensively imported and grown in that part of the 
country whence the disease appears to have spread, suggests that Eastern 
Asia may be the home of this parasite. . . . That the parasite has 
come from Europe seems less probable, in view of the fact that, according 
to Pantanelli, as well as according to my own inoculations under green- 
house conditions, the European chestnuts show no resistance to the 
disease. ; 
“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 the vicinity of New York City — Bedford county, Virginia, and 
Baltimore county, Maryland —contained-chestnut 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.” 
Clinton (1909, 1911, 1912 a, 1912 C, 1913) holds to the opposite view; 
