366 YEARBOOK OF THE DEPARTMENT OF AGRICULTURE. 
MEANS OF SPREAD AND INFECTION. 
Recent investigations show that the ascospores are commonly 
ejected during and after a rain, and on account of their small size 
may be blown by the wind for a distance of at least 50 feet, in spite 
of their sticky character. The strings of sticky conidia are instantly 
dissolved by rain, and are washed down over the surface of the tree. 
It is conceivable that they may be blown by the wind as far as rain 
or spray is blown or, mingling with dust at the foot of the tree, be 
blown about with the dust. There is strong evidence that the sticky 
conidia and ascospores may become attached to the various forms of 
animal life—insects, birds, squirrels, ete.—which frequent the diseased 
trees, and so be carried by them to other trees. That the disease is 
carried bodily for great distances in diseased chestnut nursery stock, 
unbarked ties, poles, or other timber, tanbark, etc., is a demonstrated 
fact. 
When the spores have once been carried to a previously uninfected 
tree they may develop in any sort of wound or injury in the bark 
that is reasonably moist, and produce a canker. There is, indeed, 
some slight evidence that under certain conditions the fungus may 
gain entrance through apparently uninjured bark; but it is not nec- 
essary to assume that such entrance is common in nature, for the 
bark of the typical chestnut tree is covered with all sorts of injuries 
through which the fungus can readily find entrance. 
No evidence has been adduced up to the present time to show that 
a tree with reduced vitality is more susceptible to infection or that 
the cankers develop more rapidly in such a tree than in a perfectly 
healthy and well-nourished tree of either seedling or coppice growth, 
except in those cases where such reduced vitality is accompanied by 
bark injuries through which spores can gain entrance. Nor has any 
evidence yet been adduced to show that weather or soil conditions 
within the present range of the disease exert any appreciable effect 
upon it, beyond the fact that wet weather in general favors the dis- 
tribution of the spores. 
The American chestnut, the chinquapin, and the cultivated varie- 
ties and hybrids of the European chestnut are all subject to the bark 
disease, although apparently varying in susceptibility. The Japa- 
nese, Korean, and Chinese varieties appear to show decided resist- 
ance. Unfortunately, these varieties are, so far as known, too small 
to be of value except as lawn and nut-producing trees. In America 
true examples of these varieties are rarely seen. What passes in the 
market as the Japanese chestnut, for example, is almost invariably a 
hybrid between the Japanese and some American or European 
variety. 
