224 JOURNAL OF ECONOMIC ENTOMOLOGY [Vol. 5 
reddish-brown color, which can easily be detected at a long distance. 
Later this leaf coloration changes to a more brownish tinge and the 
leaves are commonly persistent for a considerable time. The burs 
commonly persist on the tree during the following winter, thus pro- 
ducing the only symptom which is at all conspicuous during the leafless 
season. The great damage which the disease has done in the late 
summer thus becomes most evident at the beginning of the next season, 
and that done in the spring becomes evident later in the same season, 
giving rise to the false but common idea that the fungus does its work 
at the time of year that the leaves change color, when in reality the 
harm was done much earlier. 
Perhaps the most easily seen as well as the longest persistent symp- 
tom of the bark disease is the prompt development of sprouts on the 
trunk of the tree and at its base, or somewhat less frequently on the 
smaller branches (Fig. 1). Sprouts may appear below every girdling 
canker on a tree, and there are usually many such cankers. These 
sprouts are usually very luxuriant and quick growing, but rarely 
survive the third year, as they in turn are killed by the fungus. The 
age of the oldest living sprout, as determined by the number of its 
annual rings, is an indication of the minimum age of that portion of 
the infection immediately above it. Sprouts are sometimes produced 
as a result of other injuries; for instance, trees girdled by borers may 
develop sprouts, but these are generally less rapid in growth and are 
distributed with greater uniformity over the trunk. 
The disease is spread by the spores of the fungus, of which there 
are two kinds. Both kinds of spores appear to be sticky, and there 
is little evidence that they are transmitted to any distance by wind 
except when washed down into the dust and so blown about with 
it. The spores are spread easily through short distances by rain; 
particularly they are washed down from twig infections to the lower 
parts of the tree. There is circumstantial evidence that the spores are 
spread extensively by birds, and there is excellent evidence that they 
are spread locally by insects and by various rodents, such as squirrels. 
The disease is carried bodily for considerable distances in tan bark 
and unbarked timber derived from diseased trees. One of the most 
prolific sources of general infection has been the transportation of 
diseased chestnut nursery stock from infected to uninfected localities. 
When the spores have once been carried to a healthy tree, they may 
develop in any sort of hole in the bark which is reasonably moist. 
These may be wounds or mechanical injuries, but by far the most 
common place of infection is a tunnel made by a borer. Borers' tun- 
nels are usually moist, even in dry weather, and in them the spore 
finds surroundings favorable to its development. 
