ized by the appearance of microscopic,
black, short-beaked fruiting structures or perithecia that are filled
with sticky ascospores. This sexual form is a species of
_Endoconidiophora_.

The sexual form of the fungus was first found in nature in Illinois in
the autumn of 1951. The perithecia are produced on the mycelial mats
beneath the loose and sometimes cracked bark of diseased oaks. Both the
ascospores of the sexual form and the endospores or conidia of the
asexual form will cause wilt if the spores are injected into oak trees.

From the foregoing information it is apparent that several methods by
which the disease might be spread over long distances are possible.
First, and what seems to be most probable, is transmission by insects.
Adult beetles, such as the two-lined chestnut borer, which emerge from
dead trees in the spring and feed on the leaves of healthy trees might
transmit the spores of the fungus. Other insects might feed on the
fungus mats that are exposed through cracks in the bark and carry both
the sticky ascospores and conidia to other trees. Additional agents that
must be considered are woodpeckers, squirrels and air currents.

Besides searching for the vector or vectors that spread the disease
other important studies are in progress. Among these is the
consideration of chemotherapy as a possible means of controlling oak
wilt. For our purpose, plant chemotherapy may be defined as the control
of disease by chemicals which are introduced into the plant. According
to Dr. Paul Hoffman of the Illinois Natural History Survey, a number of
chemicals have shown promise in curing small diseased oak trees when
treated in a very early stage of the disease. In one instance, trees
that were inoculated with the oak wilt fungus then treated with
chemicals 2 years ago are still alive. The most promising results were
obtained by injecting the chemicals into the soil where they are taken
up by the roots and by applying chemicals directly to the foliage in a
spray. Trunk injection showed least promise because of the limited
distribution of the chemicals through the tree.

The use of chemicals for curing wilt-infected trees is still in the
early experimental stage and is not yet recommended as a practical
control measure.

In 1949 Wisconsin workers demonstrated the local spread of oak wilt
through natural root grafts. They found that the poisoning of a single
healthy tree with sodium arsenite often killed as many as