CHESTNUT BARK DISEASE. 365 
the bark may look healthy, but when hit by a hammer, it gives 
a hollow sound and is easily separated from the wood, showing 
the cambium entirely dead. After the tissues are killed, one 
is apt to find the larvae of beetles, etc., at work between the 
bark and the wood, and their presence has led some to think 
that they were the real cause of the trouble. 
The first appearance of the disease on the smooth bark fre- 
quently seems to be due to the injuries caused by bark miners, 
Plate XXIV a. The most frequent starting points, however, are 
through cracks, wounds or where a branch has been pruned, 
XXIV b, or killed from some cause, as winter injury. Very 
frequently the fungus gets a start from a crack in the crotch 
of the limbs. 
In summer time the disease is recognized in the top of the 
trees, even at some distance, by the dead leaves on certain 
branches, which have been girdled, but whose girdled area is 
not easily seen from the ground, Plate XXIIa. These dead 
leaves adhere for a long time to the branches. They first 
begin to show about the latter part of June or the first of 
July, when the previous year’s canker has finally succeeded in 
girdling the branch. In the winter these dead branches some- 
times retain their dead foliage and burs long after those from 
healthy branches have fallen. This is true, however, of a 
branch killed prematurely from any cause. 
The cankers on the main trunk, as they become serious, 
cause the latent or adventitious buds in the healthy tissues 
beneath to develop, so that in time there are produced a number 
of slender sprouts, and one can detect the presence of a canker 
high up in the tree by these. 
The fungus, while it kills the bark and cambium, and thus 
eventually the tree, is not a true wood-destroying species. 
When the trunk of a living, but cankered, tree is cut and barked, 
the cankered spot, Plate XXIIId, is usually visible as a 
darker area in the wood corresponding to the cankered spot 
in the bark, the mycelium of the fungus having injured the 
woody tissues for a short distance inward. Such cankered 
spots can sometimes be seen on telephone poles used along the 
highway. This injury in itself, however, is negligible so far as 
it affects the value of the pole. 
