516 Journal of Agricultural Research Vol. III, No. 6 
TasLE XIII.—Maximum duration of ascospore expulsion after the cessation of rain, 
as determined by the examination of slides in ascospore traps at West Chester, Pa., 
in 1913 
Maximum Maximum 
duration of : duration of 
Date. Rainfall. spore Date. Rainfall. spore 
expulsion expulsion 
after rain. after rain, 
Inches. He. im. Inches. dq. m. 
ANGs B37 5c reseeseess 0.175 AS. | OO Ptes2E adi sacsetercces 0. 43 1 58 
Sept. 18%..06ccvcsees - 26 6 15 Bidens ans . 10 40 
EQsyecrevuxaen 68 5 27 224 tan dovtawaia +73 Il 2 
BO semi ey tus - 09 13. 4.) Oct. 20.560 sccceeanes - 86 3 8 
It should be mentioned in this cénnection that the figures given 
in the Table XIII were secured in all cases, except that of October 
20, from bark that had been protected continuously by the trap slide . 
from the drying action of the wind, and it is possible that under such 
conditions the duration of expulsion may be slightly prolonged. But 
the data relative to the maximum duration of expulsion on October 20 
were secured from bark previously unprotected by slides, since seven 
perithecia in five exposed areas were found to be expelling spores after 
expulsion had ceased in all but one area protected by the ascospore traps 
(Table XII). These tests prove beyond doubt that under natural 
conditions certain exposed areas of diseased bark do remain wet enough 
to cause spore expulsion fully as long as the particular areas protected 
by the ascospore traps. Of course, such areas would usually be in 
locations more or less protected from the wind or sun; but, nevertheless, 
they would continue to act as a source of spores for wind dissemination 
as long as any expulsion was in progress. 
The direct bearing of the results of these ascospore-trap tests upon the 
results obtained in the exposure plates has been brought out in the 
discussion of the latter topic. 
ASPIRATOR TESTS 
It has already been brought out in the historical introduction that 
previous analyses of air by the aspirator method under natural conditions 
in the field during dry weather failed to show the presence of spores 
of the chestfut-blight fungus (2). Positive results were obtained, 
however, under artificial conditions in the field, and it seems probable 
that failure to detect spores under natural conditions was due to the fact 
that most of the analyses were made during dry weather. If positive 
results were obtained following periods of rain, that fact was not brought 
out in the discussion (2). In order to obtain definite information on this 
point, the aspirator tests reported in the following pages were made so as 
to include the filtration of air immediately following periods of rain, 
as well as during the intervening dry weather. 
METHOD OF MAKING THE ANALYSIS 
The apparatus used in this series of tests consisted of a 4-liter aspirator 
bottle set on a level stump near the center of the field (fig. 1). The 
nearest trees were 15 feet north, 19 feet east, and 33 feet west, and the 
