CHESTNUT TREE BLIGHT. 23 
it. Sprouts are sometimes produced as a result of other injuries; 
for instance, trees girdled by borers may develop sprouts, but these 
are generally less rapid in growth and ‘are distributed with greater 
uniformity over the trunk. 
MEANS OF SPREAD AND ENTRANCE. 
The disease is spread by the spores of the fungus, of which there 
are two kinds. As both ind of spores appear to be sticky, there 
is no evidence that they are transmitted by wind except where they 
may be washed down into the dust and so blown about with the 
dust. The spores are spread easily through short distances by rain; 
articularly they are washed down from twig infections to the 
ower parts of the tree. There is strong evidence that the spores 
are spread extensively by birds, suporialls woodpeckers, and there 
is also excellent evidence that they are spread by insects and by 
various rodents, such as squirrels. The disease is carried bodily for 
considerable distances in tan bark and unbarked timber derived from 
diseased trees. One of the most prolific sources of general infection 
has been the transportation of diseased chestnut nursery stock from 
infected to uninfected localities. 
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 asso- 
ciated 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 beets 
does not result in or is not accompanied by bark injuries throug 
which spores can gain entrance. 
Tar 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 
