Mar. as, r9r5 Dissemination of Chestnut-Blight Fungus 515 
SUMMARY OF ASCOSPORE-TRAP TESTS 
From the standpoint of wind dissemination, the all-important feature 
proved beyond doubt by these tests is that in every case where ascospore 
expulsion occurred at all it continued for a time after the cessation of the 
rain, thus insuring a supply of spores in the air. 
A glance over these results shows that in a general way the volume of 
ascospore expulsion, as measured by the character and number of spots 
on the slides, is greatest during or shortly after the rain and decreases 
more or less uniformly as the bark dries. On August 27 the rains were 
of the thunderstorm type, being of very short duration, and consequently 
the perithecia had hardly been wet for a sufficient length of time when the 
rain ceased. The greatest volume of expulsion occurred, therefore, a little 
later, evidently between 15 minutes and 1 hour after the rain had ceased. 
With the exception of the rain in the afternoon of September 21, the 
tests of September 18, 19, 20, 21, and 22 are rather unsatisfactory, since 
no records could be obtained until some time after the rain had ceased. 
‘The summary for these dates (Table XI) shows that the maximum vol- 
ume of spore expulsion had occurred before the first collections were 
made, and whether the climax occurred during the rain or shortly after- 
wards can not be stated. In the case of the afternoon rain of September 
21 very evidently the maximum volume of spore expulsion took place 
before 33 minutes had elapsed after the cessation of the rain. 
On October 20, after the bark had been thoroughly saturated by a rain 
in the night, the greatest volume of expulsion occurred within one hour 
after the rain. ‘Two hours and nine minutes later a light rain of 58 min- 
utes’ duration began, and the results secured after this shower (Table XI) 
show that in three traps tested the greatest volume of expulsion occurred, 
not during the rain, but after 22 to 43 minutes had elapsed since its ces- 
sation. 
As to the rate of subsidence of ascospore expulsion after the rains, 
Table XI shows a marked contrast between the results obtained on differ- 
ent dates. This has been mentioned in the discussion of the exposure 
plates and the relation of the subsidence of ascospore expulsion to 
weather conditions. In the cases of September 18, 19, 20, and 22 the 
duration of expulsion is seen to have been prolonged after the rains, and 
in all cases except September 19 the data show that the rate of subsidence 
was very gradual. Except for the last three hours of the duration of 
expulsion on September 22, fog or cloudiness and low wind prevailed, 
and the weather conditions were not favorable to rapid drying of the bark. 
After the rains of September 21 and October 20 the rate of subsidence 
of ascospore expulsion was relatively abrupt and rapid, and its duration 
was comparatively short, especially after the second rain on September 21. 
Here, again, the relation of duration of expulsion to rapidity of drying of 
the bark is shown, since the rains on these dates were followed by brisk 
winds, and, except for the second rain of September 21, by: rapid clearing 
and sunshine. Such weather conditions were, of course, very conducive 
rapid drying of the bark. 
arte ee A A aration of ascospore expulsion as determined by these 
tests after each of these rains is shown in Table XIII. In considering 
these data the weather conditions just described should be borne in mind. 
78745°—15——6 
