5i6 



Journal of Agricultural Research 



Vol. III. No. 6 



Table 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 igi3 



It should be mentioned in this connection 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 chestnut-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 drv 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. i). The 

 nearest trees were 15 feet north, 19 feet east, and 33 feet west, and the 



