eared of all diseased trees. It is therefore possible that insect
vectors or other agencies may have spread the disease to the scions of
the topworked seedlings from the infected heartnut and butternut trees.

Number 795 is the only _J. nigra_ tree on the station farm that has
consistently shown symptoms of the disease during the past eight years,
and in 1950 only a few limbs are affected. On the basis of the
admittedly meager information reported here, it can be stated that the
black walnut varieties used in these experiments are more resistant to
the bunch disease than are varieties and seedlings of heartnut and
butternut. That this is generally true is also borne out by the fact
that in the vicinity of Beltsville, Maryland, and the District of
Columbia, practically all dooryard trees of the Japanese walnut are
infected with bunch disease, many of them having already been killed,
whereas relatively few black walnut trees in the area show symptoms of
the disease.

The suggestion has been made that most varieties and seedlings of black
walnut are symptomless carriers of the disease, and only under certain
adverse conditions of environment would symptoms appear. This would
explain why trees that are cut back severely, as was the case with tree
Number 838 described above, show symptoms on the excessively vigorous
shoots of the next year's growth.

Little can be said at the present time about the relative resistance of
black walnut varieties to the bunch disease because nothing is known
about how it is spread from one individual tree to another. The case
histories of trees described in the present paper are considered to be
worth recording because they show that black walnut trees may support
diseased scions and later regenerate apparently healthy tops. In these
cases the trees showed a type of resistance to the disease. However,
there are many cases known, the majority of which are seedlings, in
which black walnut trees became so badly infected with the disease that
nut production ceased and the trees later died. Whether the type of
resistance described in this paper is widely prevalent in the black
walnut as a species will be impossible to determine until more is known
about how the disease is spread.

FOOTNOTES:

[Footnote 13: Several common names have been applied to this disease,
among which "bunch" and "brooming" have most frequently been used. The
authors strongly feel that the accepted common name should be "b