10 CONTROL OF THE CHESTNUT BARK DISEASE. 
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 bark borers, and particularly the two-lined chestnut borer 
(Agrilus bilineatus), are directly associated in this way with 90 
per cent or more of all cases of this disease. We are informed that 
the Bureau of Entomology will issue a circular on the insects as- 
sociated with the chestnut bark disease. 
The writers have no definite evidence, experimental or other- 
wise, to show that a tree with reduced vitality is more susceptible 
to infection, or that the disease spreads more rapidly in such a 
tree, than in a perfectly healthy and well-nourished tree of either 
seedling or coppice growth, provided that such reduced vitality 
does not result in or is not accompanied by bark injuries through 
which spores can gain entrance. 
THE CONTROL OF THE DISEASE. 
ELIMINATION AND QUARANTINE. 
FUNDAMENTAL OBSERVATIONS AND EXPERIMENTS. 
No method of immunizing individual trees against the bark dis- 
ease is yet known, and no method of treating or curing them when 
once attacked is certain in its results. While this is unfortunate 
from the standpoint. of the owner of orchard trees. and large orna- 
mental trees of great individual value, no method of dealing with 
single trees—surgery, medication, spraying, etc.—however successful 
in itself, would meet the demands of the present situation. It is not 
practicable at present to apply any individual method of treatment 
to forest trees; the individual tree is not worth it, and will not be 
for many years. Therefore, so far as the chestnut forests are con- 
cerned we do not need to regret particularly that no individual 
treatment has yet been discovered that is entirely effective. 
Fortunately, however, there is a method of dealing with the situa- 
tion which is applicable to the country as a whole and which, so 
far as tested, is practicable. Early in the course of the writers’ 
investigations it became evident that the disease advances but slowly 
in a solid line, but instead spreads from isolated centers of infec- 
tion, often many miles in advance of the main line of disease. 
That such is the case is evident from a glance at figure 1. It there- 
fore seemed probable that if these advance infections could be lo- 
cated at a reasonably early stage, they could be eliminated at rela- 
tively little expense, thus preventing further spread from these 
467 
