INFLUENCE OF CERTAIN CLIMATIC FACTORS II 
the curve of growth makes it seem almost impossible that either total 
amount of rainfall or number of days with rain has any direct effect 
on the growth of the fungus. This is theoretically very probable 
since the growing edge of the fungus is in or near the cambium of the 
host under the bark and its moisture supply must come from the host 
itself. 
It is conceivable that a fungus might be susceptible to changes in 
the water content of those portions of its host in which it grows, so 
slight as not to produce a perceptible effect on the host. There is, 
however, no evidence that such is the case in Endothia parasitica. On 
the other hand Rankin (9, p. 245) who investigated the relation of 
the growth of Endothia parasitica to the water content of the bark of 
Castanea dentata during the summer of 1912 at Napanoch, N. Y., 
failed to demonstrate that the "variation in the physiology of the 
tree which results from drought conditions alters to any great degree 
either the susceptibility of the chestnut tree or the rate of progress 
of the mycelium in the bark." 
With his conclusion the writer's observations entirely agree. In 
the course of three years' inoculation experiments and field observa- 
tion the writer has been unable to obtain any evidence that the rate 
of growth of this fungus is affected by external dryness which does fiot 
produce a perceptible withering effect on the host. 
Length of Frostless Season 
The only remaining factor seems to be that of temperature. Zon 
(13) has emphasized the necessity of considering the length of the 
growing period in plant climatology and the advisability of tabulating 
climatic data separately for the period of growth and the period of 
rest. While his contention is undoubtedly correct for green plants 
it is apparently not true in the case of Endothia parasitica which has, 
strictly speaking, no resting season. Field observations and laboratory 
experiments both show that Endothia parasitica will grow whenever 
the temperature rises above its minimum for growth, which, as Shear 
and Stevens (11, p. 7) have determined, is about 8° or 9° C. This is 
apparently true regardless of the previous temperature and whether 
the host is dormant or not. 
Anderson and Rankin (3, p. 574) conducted experiments separately 
at Charter Oak, Pa., and Napanoch, N. Y., and agree that the chief 
growth of Endothia parasitica occurs between March and October but 
