STEVENS: PREVALENCE OF ENDOTHIA GYROSA 143 
The temperature of the Southern States is undoubtedly more 
favorable for the growth of E. gyrosa than that of the states farther 
north. 
The northern boundary of the region where this fungus is 
abundant does not, however, agree closely with that of any of 
the temperature regions. 
It is not perceptibly more abundant in the areas of nine to 
twelve months vegetation than it is in areas of seven months 
vegetation. 
Much of the area where E. gyrosa is abundant is in or south 
of the region of 25 inches rainfall, April to September, inclusive. 
It is, however, very abundant in Tennessee, Kentucky, and 
Indiana, where the rainfall is less than 25 inches for this period. 
Although there are no sudden changes in climate in going from 
north to south in the eastern United States, there is a fairly 
definite division into an area where E. gyrosa is abundant and an 
area where it is rare. 
This seems to indicate that factors other than climate affect 
the prevalence of this fungus. 
The chief factor in the greater abundance of E. gyrosa seems to 
be increased opportunity for infection. 
Opportunity for infection is much greater in the Southern 
States than in the Northern because of the larger number of host 
species and their greater importance relative to other species. 
Opportunity for infection is still further increased by the soil 
and cultural conditions which cause greater erosion and leave 
large numbers of roots of Fagus and Quercus exposed and subject 
to injury. 
BUREAU OF PLANT INDUSTRY, 
WasuHInGTon, D. C 
LITERATURE CITED 
1. Brooks, C. F. The snowfall of the eastern ache States. Mo. 
Weather Rev. 43: 2-11. f. 1-13. Ja19 
2. Davis, R. O. Soil erosion in the south. u S. Dept. Agr. Bull. 
180: 1-23. pl. 1-9. Ap 1915. 
3. Frothingham, E. H. The northern hardwood forest: its composi- 
tion, growth and management. U. S. Dept. Agr. Bull. 285: 
1-80. pl. I-14. 1915. : 
