134 STEVENS: PREVALENCE OF ENDOTHIA GYROSA 
probably the greater rainfall, especially during the growing season. 
The rainfall of the eastern United States during the growing season 
is given by Henry (5). In general, the area where E. gyrosa is 
abundant is largely in or south of the region of twenty-five inches 
rainfall, April to September, inclusive. An exception to this is 
found in Tennessee, Kentucky and southern Indiana, which are 
well outside the area of twenty-five inches rainfall, but where E. 
gyrosa is fullyas abundant as in the region of over thirty inches 
rainfall. 
The striking fact has recently been pointed out by Ward (11), 
that in the eastern United States no sudden changes in climate are 
met with in going from north to south, but the transitions are 
everywhere slow and gradual. On the other hand, there is a 
fairly definite line of demarcation between the area in which E. 
gyrosa is abundant and the area where it is rare. This seems to 
indicate that factors other than temperature and rainfall markedly 
affect the prevalence of this fungus. 
That E. gyrosa is abundant in southern iaginns where the 
climate ‘is both drier and cooler than in most regions where the 
fungus is commonly found, seems to be due to greater opportunity 
for infection. As has been pointed out in an earlier paper (8), 
southern Indiana is a stock-raising region where pastures contain- 
ing beech trees arenumerous. Nearly all of the collections of E. 
gyrosa in this region were found in such pastures on the roots of 
beech which had been injured by cattle.. The importance of such 
opportunity for infection is emphasized by the condition found 
at Columbiana, Ohio, in June, 1913. This locality is several 
hundred miles outside the area in which E. gyrosa is commonly 
found in abundance, yet in a single pasture where there were 
from fifteen to twenty large beech trees many of whose roots were 
exposed and had been injured by trampling of cattle, the writer 
found this fungus abundant in more than twenty small patches. 
OPPORTUNITY FOR INFECTION 
Field observations have convinced the writer that opportunity 
for the infection of its hosts is of the greatest importance in deter- 
mining the prevalence of EZ. gyrosa and that the greater abundance 
of E. gyrosa in the southern states is largely accounted for by the 
