INFLUENCE OF CERTAIN CLIMATIC FACTORS 
29 
is little difference in the temperature of the three summers, although 
1913 was somewhat warmer than the others. Both 1913 and 1914, 
the years in which no perithecia were produced, had a decided drought 
in the fall months. 1915, on the other hand, when perithecia appeared 
abundantly by September, had 7 inches of rainfall in August. In this 
locality, as in Ulster County, New York, perithecia appeared following 
a period of abundant rainfall and failed to appear in dry weather. It 
is somewhat surprising that perithecia failed to appear in August, 1914, 
since the months in Washington had a larger rainfall than the fall 
months of 1912 in Ulster County. On the other hand, the temperature 
was much higher in Washington during August, 1914, and the humidity, 
therefore, presumably lower. This would indicate that it is humidity 
rather than rainfall as such that determines the production of peri- 
thecia. These data are in accord with the assertion originally made 
by Metcalf (7) that in dry weather spore production was reduced and 
that dry seasons checked the progress of the chestnut blight. 
On comparing the climatological conditions at the two stations 
for the three years during which observations were made, it is evident 
that those years in which most ascospores were produced were the 
years of most abundant rainfall and largest number of days with rain 
regardless of temperature. If these conclusions are correct, tem- 
perature has very little relation to the production of ascospores by 
Endothia parasitica, whereas amount of moisture in the air has a 
determining relation. This is probable on theoretical grounds since 
perithecia develop on the dead tissues of the canker separated by a 
considerable distance from any living tissues of the host, so that 
moisture which reaches the developing perithecia must necessarily 
come from the air. 
Summary 
A quantitative comparison of the available climatic data with the 
growth and fructification of Endothia parasitica at various points from 
southern New Hampshire to central Virginia has been made. 
The area covered includes the northern limits of growth of other 
species of Endothia and is a transition region for several important 
plant diseases. 
Eleven stations, extending through five degrees of latitude, were 
chosen, as well as a series of stations at different elevations on Overlook 
Mountain in the Catskills. 
The stations were visited regularly during the summer of 1914. 
