278 



THE MONTHLY BULLETIN. 



CAUSE OF THE DISEASE. 

 The disease is caused by a parasitic fungus, Endothia parasitica, which belongs 

 lo the Ascomycetes. The fungus gains an entrance through a wound in the bark and 

 spreads more or less concentrically in all directions from this point (Fig. 84). It 

 -rows typically in the living bark of the chestnut, from where it is able to penetrate 

 into the outer layers of the sapwood. The effect of the fungus on the chestnut soon 

 becomes visible in the shape of dead patches or cankers. When these cankers have 

 extended all around the stem or branch, the complete girdling kills off everything 

 above. In this way whole trees may be destroyed within one season. 



Fig. 83. — Chestnut orchard. The tree In the foreground has been killed 

 during the last season, as shown by the persistent burs. 



On young shoots the affected areas show rather conspicuous discolored sunken 

 patches surrounded by the olive-colored normal bark from which they occasionally 

 are separated by a raised margin. On older bark the patches are not as clearly 

 recognizable. On peeling off the dead bark the mycelium— that is, the vegetative 

 body of the fungus plant — appears in form of small white flakes, or later, in form of 

 yellowish flat, distinctly fan-shaped masses. These "fans" are highly characteristic 

 and serve as an excellent criterion in the determination of the chestnut bark fungus. 



The means of propagation of the fungus from tree to tree are very simple. They 

 consist of two forms of spores, the pycnospores and the ascospores. The cankers or 

 dead areas are usually covered with innumerable small pustules of yellow, orange or 



