ENDOTHIA PARASITICA AND: RELATED SPECIES. 53 
factor in determining their distribution. As already stated, while 
Endothia fluens occurs on Quercus, it has been found toward the 
southwestern limit of its range (northern Mississippi and Alabama) 
only on Castanea, and in Tennessee the writers have sixteen collec- 
tions of this species on Castanea and only three on Quercus. In 
this same region, E’. gyrosa is everywhere abundant on Quercus. In 
numerous inoculations with #. gyrosa and FE. fluens on oak it has 
been found that /’. gyrosa is more generally successful than EZ. fluens. 
Moreover, £. gyrosa occurs abundantly on Liquidambar and Fagus 
in this region, thus providing more numerous sources of infection 
for this species than for Z’. fluens. It seems highly probable, there- 
fore, that E. gyrosa, with its greater affinity for oak and greater 
opportunity for infection, may occupy the available oak roots to 
the exclusion of Z. fluens, even though climatic conditions are favor- 
able for the growth of the latter species. Castanea rarely serves as 
a host for E’. gyrosa; consequently, on this host Z’. fluens meets with 
little competition and is very abundant. 
In the northeastern limit of its range, Endothia fluens has been 
found only on oak roots. Whether it grows naturally on chestnut 
in this region can not well be determined, since practically all the 
chestnut trees here are dead or badly diseased with E. parasitica. 
E. gyrosa is rare in this region, but E'. flwens here evidently comes 
into competition with Valsa frustum-coni (Schw.) Curtis, which is 
common on exposed roots of various species of Quercus. 
CLIMATE, 
Since none of the species of Endothia in America extends to the 
limits of its host species, climate probably has an important part in 
determining their present ranges. 
In this connection it is of interest to compare several life zone and 
climatic maps which have been published with the range maps of 
the various species of Endothia. The map entitled “ Life zones of 
the United States,” by C. Hart Merriam (50, pl. 14), is based largely 
on a study of animal life. Merriam deduces from his studies the 
conclusion that the northward distribution of animals and plants is 
determined by the total quantity of heat and their southern dis- 
tribution by the mean temperature of the hottest part of the year. 
The life zones which he outlines show, however, a striking relation 
with the known ranges of Endothia in America. With the exception 
of a single locality for Endothia gyrosa in Michigan, all the known 
localities for EZ. gyrosa and E. fluens fall within the Upper Austral 
and Lower Austral zones. All the known localities for FE. fluens and 
all the region where Z. gyrosa has been found abundantly fall within 
the humid divisions of these zones. The northeastern limits of the 
Upper Austral coincide very closely with those of Z. gyrosa; its 
