Mar. 25, r915 Dissemination of Chestnut-Blight Fungus 511 
occurs only when the perithecia-bearing bark has been wet by rains, the 
following facts are presented to show that wind dissemination is directly 
dependent upon weather conditions causing spore expulsion. 
Of the total number of 756 plates exposed during these tests 95 were 
exposed while ascospore expulsion was known to have been in progress, 
and of these, 41 yielded colonies of Endothia parasitica. Of the remaining 
661 plates exposed at other times than those noted above, but 23 yielded 
colonies of E. parasitica, and 14 of these were exposed within 12 hours 
after expulsion was known to have occurred. 
To bring out in a more striking manner the relation of rain to wind 
dissemination, it is worthy of note that out of a total of 427 ascospores of 
Endothia parasitica caught in the exposed plates 402, or 94 per cent, were 
caught in plates exposed while spore expulsion was known to have been 
in progress, and of the remaining 25 spores 3 were caught within 5 hours 
after the cessation of a rain (Sept. 8) and 12 more were caught within 12 
hours after ascospore expulsion was known to have occurred. This 
leaves but 10 out of 427 spores, or 2.3 per cent, seeming to be stray 
ascospores bearing no relation to a rain. 
As to the origin of the 22 colonies of Endothia parasitica appearing in 
plates exposed when spore expulsion was known not to be in progress 
(see Table II), the following points are cited to prove that they originated 
from stray ascospores which, after expulsion, lodged on near-by or, per- 
haps, distant trunks, limbs, or leaves and were subsequently loosened 
by the mechanical action of some agency. 
1. All but one of the 21 plates containing these colonies yielded only 
a single colony of Endothia parasitica each. 
2. In one colony a fragment of bark was visible at its center. 
3. All except one of these spores were caught at stations more or less 
overhung by branches of diseased trees, and all except three were caught 
on stumps surrounded by sprouts. 
4. Only 1 out of 192 plates exposed at unsheltered stations when 
expulsion was not in progress yielded a colony of Endothia parasitica. 
If these had been stray spores that were still floating in the air since 
expulsion, they would have fallen just as frequently into plates exposed 
out in the open at unsheltered stations. During a period of ascospore 
expulsion following a rain it seems probable that the spores would not 
all be swept away by air currents but that some few would find lodgment 
upon near-by leaves and branches. Such lodgment is especially likely 
to take place if there is no noticeable wind when expulsion is in progress. 
Thus, it seems quite probable that the colonies obtained when perithecia 
were not active originated from spores dislodged from either healthy or 
diseased parts of trees more or less overhanging the plates. : 
Unless attached to a bark fragment, the path of these spores in falling 
would not necessarily approach the vertical, and such spores might be 
transported by the wind just as readily as though they were freshly 
expelled. This explains, perhaps, why one spore was caught in plate 
‘No. 5037, exposed 27 feet from the nearest chestnut tree. The probable 
reason, then, why, with this exception, such stray spores were caught 
only under trees is that the rareness of their occurrence in the air pre- 
vented their detection elsewhere than in very close proximity to their 
place of temporary lodgment, since with the exposure-plate method the 
chance of detecting these spores decreases very rapidly as the distance 
from their source is increased. 
