STEVENS: PREVALENCE OF ENDOTHIA GYROSA 133 
1915, Endothia parasitica made almost twice the lateral growth 
on Castanea dentata in Virginia that it made in New England. 
This difference in growth is closely correlated with the difference 
in temperature of the two regions. It seems very probable, 
therefore, that the more favorable temperature of the Southern 
- States favors the more abundant growth of E. gyrosa in that region. 
A comparison of the map (Fic. 1) of the distribution of E. 
gyrosa with climatic maps shows certain general correlations. 
Much of the region where E. gyrosa is most abundant lies south 
of the isotherm of 6,000 temperature summation and the closely 
similar isotherm of 600 temperature efficiency as calculated by 
the Livingstons (7). Much of the region where E. gyrosa is most 
abundant lies within or south of the area of eight months (April 
to November) vegetation, as mapped by Zon (12). 
It is significant, however, that the area in which EF. gyrosa is 
abundant does not agree closely with any of these lines. The 
fungus is abundant considerably north of the line of 600 tempera- 
ture efficiency in Kentucky and southern Indiana but falls far 
short of this isotherm in eastern Virginia. The same relation 
exists between the area in which FE. gyrosa is abundant and_ the 
isotherm 10,000 as given by Livingston (6) in his chart based on 
physiological summation indices of temperature efficiency for 
plant growth (6, f. 2). Similarly, the northern limit of the area 
of abundance coincides closely with the limit of eight months 
vegetation in Virginia, but runs well toward the middle of the area 
of seven months vegetation in Kentucky and Indiana. Moreover, 
as has been stated above, the temperature of New England in the 
region of six months vegetation is evidently sufficient for the 
growth of E. gyrosa under some circumstances. 
On the other hand, Endothia gyrosa is not perceptibly more 
abundant in the areas of nine to twelve months vegetation, i. e., 
southern Mississippi, Alabama, and Florida, than it is in certain 
portions of the area of seven months vegetation, i. e., Kentucky 
and southern Indiana. It would seem then that temperature 
alone is not very significant in determining the abundance of this — 
fungus. 
Precipitation—One of the most important climatic factors 
influencing the abundance of E. gyrosa in the Southern States is 
