76 MASSACHUSETTS HORTICULTURAL SOCIETY 



quick growing, but rarely survive the second or 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. This development of sprouts, 

 sometimes continuing vigorously for at least five years after the 

 death of a tree, affords clear evidence of the healthy condition of 

 the roots.^ 



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' tunnels are moist, even in dry weather, and in them the 

 spore finds surroundings favorable to its development. In many 

 parts of the country where the disease is prevalent there is very 

 direct evidence that insects are definitely associated in this way 

 with 90 per cent or more of all cases of this disease. 



The Species Affected. 



So far as is now known, the bark disease is limited to the 

 true chestnuts — that is, to the members of the genus Castanea. 

 The American chestnut, the chinquapin, and the cultivated varie- 

 ties of the European chestnut are all readily subject to the disease. 

 Only the Japanese (15) and, according to the experience of Dr. 

 Robert T. Morris (16), the Korean and Chinese varieties appear 

 to show decided resistance. In spite of popular reports to the 

 contrary, it can be quite positively stated that the bark disease 

 is not now known to occur on the living portions of oaks, horse- 

 chestnuts, beeches, or hickories. The golden-leaf chinquapin 

 (Castanopsis chrysophylla) has shown under greenhouse conditions 

 absolute resistance to inoculations. That Diaporthe parasitica may 



' At this point tlie speaker introduced 40 lantern slides, descriptive of various 

 pliases of tlie chestnut bark disease. As it is impracticable to reproduce this 

 portion of the lecture without figures, reference is made to publications already 

 issued that contain illustrations of the disease (12, 13, 14), also to a forthcoming 

 bulletin of the Bureau of Plant Industry. 



