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 XXII a. 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 XXIII d, 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. 



