Mar. 25, rors Dissemination of Chestnut-Blight Fungus 509 
it should also be noted that on September 20 (Table IT), when foggy 
weather followed the rain, spores were prevalent in the air during at least 
five hours after the rain had ceased. 
A glance at the figures representing the number of spores falling each 
minute on a surface equal to 1 square foot shows that during periods of 
one to four or more hours after a rain—in other words, during such time 
as expulsion continues—healthy trees among diseased ones would be sub- 
ject to infection, since some of the ascospores would find lodgment upon 
exposed parts of trunks and branches. 
The results obtained in the early morning of September 20 by making 
exposures in an open field at varying distances from the principal source 
of spores (figs. 2 and 3) are presented in Table VIII. 
TaniE VIII.—Relation of distance from source of spores to number of spores falling on 
an area of I square foot per minute in 1913 at West Chester, Pa.% 
Number of 
Distance spores falling 
Plate No. Time. from source of | on an area of 
spores. zr square foot 
per minute. 
Feet. 
5044 | 6.03 a. m. 27 24. OF 
5045 | 6.14a.m. 85 12. 52 
5046 | 6.18 a. m. 180 6. 5 
5042 | 5.55 a.m. 266 9.51 
5047 | 6.20 a. m. 409 g. 30 
5041 | 5.504. m. 414 8. 71 
@ Plates exposed on Sept. 20, 1913. 
These exposures, all made within about half an hour and in the same 
general direction from the plot of diseased trees—i. e., the direction 
toward which the wind was blowing—show that in a general way the 
number of spores falling upon equal surfaces in equal intervals of time 
decreases as the distance from the source of spores is increased. The fact 
alone that in an open field at rather long distances from diseased trees 
ascospores were prevalent in the air to such an extent that every minute 
from 6 to 24 spores were settling upon a surface equal to 1 square foot 
(Pl. LXIII, figs. 1 and 2) indicates that at such a time many opportunities 
would be offered for exposed parts of undiseased trees at considera- 
ble distances from diseased ones to become infected by wind-borne 
ascospores. ; ; 
Furthermore, these results show that the maximum distance over 
which ascospores might be transported by the wind was by no means 
obtained, and the large numbers found at the longest distances in this 
experiment, given in Table VIII, when a light wind prevailed, indicate 
that even with a relatively light wind ascospores are probably conveyed 
istances far greater than these. ; 
: Ina conedeuict of the exposure plates yielding the high numbers of 
colonies of Endothia parasitica it is interesting to note the relatively 
large proportion of the spore content of the air formed by ascospores of 
this fungus at certain times (Table IX). 
