ENDOTHIA PARASITICA AND RELATED SPECIES. 51 
search. At the northeastern limit of £. gyrosa, Clinton (15, p. 79) 
found only a single specimen after two years’ search, and the wrilane 
have looked for it in all the other New England States without find- 
ing a single specimen. The report of Z. gyrosa from Massachusetts 
by Hitchcock (42, p. 63) has already been shown to be a probable 
error in identification. 
FACTORS INFLUENCING DISTRIBUTION. 
HOST RELATIONS. 
Just what determines the present ranges of the species can not, of 
course, be positively decided, but some relation to certain external 
factors may be traced. Neither species has the same distribution as 
Fic, 3.—Outline map of the United States, showing the distribution of Hndothia fluens 
mississippiensis and E. singularis. The dots indicate collections of F. fluens mississippt- 
ensis and crosses indicate collections of HL. singularis. 
its hosts. Quercus and Fagus are both abundant farther north than 
Endothia gyrosa has yet been found, while Quercus is abundant 
north and south of the known range of Z. fluens. It may be worthy 
of note, however, that Z. gyrosa extends north as far as Liquidambar 
is found. Perhaps more significant is the relation of the range of 
E. fluens to that of the chestnut. As will be seen from a comparison 
of the maps (figs. 2-4), Z. fluens is not found abundantly at any point 
outside the natural range of the chestnut. Especially interesting is 
the fact that the southeastern limits of Z. fluens and Castanea den- 
tata are practically coincident, for in this region Endothia fluens 
was found only on Castanea, never on Quercus. This suggests the 
possibility that Castanea may be the original and favorite host of 
Endothia fluens. 
