standpoint of disease.

The chestnut disease: The disease which is threatening the destruction
of all the chestnut trees in America is a fungus which has, within
recent years, assumed such vast proportions that it deserves special
comment. The fungus is known as _Diaporthe parasitica_ (Murrill),
and was first observed in the vicinity of New York in 1905. At that
time only a few trees were known to have been killed by this
disease, but now the disease has advanced over the whole chestnut
area in the United States, reaching as far south as Virginia and as
far west as Buffalo. Fig. 111 shows the result of the chestnut
disease.

The fungus attacks the cambium tissue underneath the bark. It enters
through a wound in the bark and sends its fungous threads from the
point of infection all around the trunk until the latter is girdled
and killed. This may all happen within one season. It is not until
the tree has practically been destroyed that the disease makes its
appearance on the surface of the bark in the form of brown patches
studded with little pustules that carry the spores. When once
girdled, the tree is killed above the point of infection and
everything above dies, while some of the twigs below may live until
they are attacked individually by the disease or until the trunk
below their origin is infected.

All species of chestnut trees are subject to the disease. The
Japanese and Spanish varieties appear to be highly resistant, but
are not immune. Other species of trees besides chestnuts are not
subject to the disease.