494 Journal of Agricultural Research Vol, III, No. 6 
and suggests that under natural conditions infection may be spread short distances 
by the wind. 
The second possibility is brought out by Metcalf and Collins (11), as 
may be noted in the following quotation: 
As both kinds of spores appear to be sticky, there is no evidence that they are trans- 
mitted by wind except where they may be washed down into the dust and so blown 
about with the dust. 
While it has not yet been demonstrated that pycnospores are carried 
in this way, the tests of Heald and Gardner (7) on the longevity of pycno- 
spores in soil give added plausibility to the theory, since these spores were 
found to persist in the soil between periods of rain and were able to 
withstand complete desiccation in the laboratory for months. 
‘Attention was first directed to the strong probability of wind dissem- 
ination of ascopores by Rankin (14), who reported their forcible ex- 
pulsion. In a later report the same writer (15) makes the following 
statement : 
Under moist conditions the ascospores are shot forcibly out in the air where they 
can be caught up by the wind and carried for a considerable distance. The speaker 
found ascopores being shot from mature pustules during every rainy period last sum- 
mer. * * * The question at once arises, Why could not these ascospores once shot 
into the air be carried long distances and, owing to their abundance, cause a large 
majority of the infection? 
After carrying out field experiments during the summer of 1912, 
Rankin (16), referring to ascospores, says: | 
They are shot out in vast numbers with every rain during the summer and are 
carried by the wind. 
Detailed field work on dissemination was carried out by Anderson (1) 
and his assistants for the Pennsylvania Chestnut Tree Blight Commission 
(2). These publications confirm the statement of Rankin that expulsion 
of spores takes place only when the pustules are moist. The seasonal 
duration of shooting under natural conditions was not determined, as the 
field tests were confined to the month of August. Under artificial con- 
ditions in the laboratory, the time required for moistened bark bearing 
perithecia to begin the expulsion of spores was determined, the shortest 
time recorded being three minutes. 
The duration of the shooting period following a rain was determined 
by artificial tests in either the field or laboratory, performed by soaking 
the specimens or drenching cankers with water. The maximum dura- 
tion recorded was five hours and two miniutes. While these tests under 
artificial conditions gave suggestive results, they were not necessarily a 
reliable indication of what would happen under natural conditions. 
It was also determined that bark kept constantly moistened continued . 
to expel spores for a maximum period of 25 days, and the point was 
emphasized that no continuous rainy weather would be longer. The 
fact that ascospores expelled during a rain would be washed down to 
