INFLUENCE OF CERTAIN CLIMATIC FACTORS 
17 
degree of correlation between the curves of growth and of temperature 
is remarkably close. In general the correlation is slightly less perfect 
when the effect of temperature is expressed by efficiency indices than 
by direct summation. In either case, there can be little doubt that 
under climatic conditions in which the optimum temperature of the 
fungus is rarely greatly exceeded (11, p. 9) the amount of growth made 
by Endothia parasitica depends directly on the amount and duration 
of heat available. If this conclusion is correct the chestnut blight 
may be expected to spread somewhat faster in the future than it has 
in the past unless other factors intervene to check its growth. For 
instance, the temperature summation for Corinth, Miss, (year ending 
June I, 1 91 5), where there is still some chestnut and where Endothia 
fluens mississippiensis was first collected, is 6,561 or 102.0 percent of 
the summation at Charlottesville. The efficiency at that point is 
764 or 120.3 percent of that at Charlottesville. The chestnut blight 
should then be able to make at Corinth a growth somewhat greater 
than that at Charlottesville and considerably greater than that at 
any of the northern points. 
At first glance the statement that the amount of lateral growth of 
Endothia parasitica is dependent directly on temperature may seem 
so simple an explanation as to be artificial. A consideration of the 
conditions under which the advancing edge of the mycelium lives in 
the host shows, however, that the biological conditions are unusually 
constant and that the fungus is very little influenced by many factors 
of great importance to green plants. 
The environmental factors most used in such a classification of 
plants as that given by Koppen (4), for instance, are many of them 
negligible. The chemical nature of the medium in which the fungus 
grows parasitically must be fairly constant since it is always the same 
portion of the same host species. Certainly the difference between 
individual trees of this species is so slight that as yet no tree resistant 
to this fungus has been found. 
Light, so important in the growth of green plants, is negligible 
here. The writer has thus far been unable to demonstrate that light 
had any effect on the growth or reproduction of this fungus under 
laboratory conditions and in all probability no light whatever reaches 
the advancing edge of the mycelium under the bark. 
The fungus has, moreover, no resting season. It is almost inde- 
pendent of external moisture supply since it lives in the portion of the 
