moved from the
tree early in 1945 and the living shoots used for scionwood in
transmission studies by the Division of Forest Pathology.

An additional case is _Tree Number 795_. This is a grafted tree of the
Graham variety of black walnut that was planted in 1932 within 100 feet
of trees of the Bates and Faust varieties of heartnuts. By 1940 the
latter trees were heavily infected with bunch disease, but it was not
until 1943 or 1944 that symptoms were discovered in the Graham tree. At
this time the heartnuts were removed from the orchard. The Graham tree
has shown only a few small diseased limbs during the past six or seven
years, and in 1950 a fair crop of nuts is in prospect.

Discussion

The following observations should be mentioned briefly before discussing
the questions raised by the case histories:

1. Out of more than one hundred seedling scions from 13 hybrids
topworked on large _nigra_ trees, three have become diseased the
first or second year after the scions began to grow on black walnut
stock.

2. The three susceptible seedlings have all been grafted on
different _nigra_ stock trees, and the three stock trees have since
regenerated only healthy limbs, after removal of the diseased
shoots.

3. Seedlings from a total of 13 natural hybrids between _J. nigra_
and _J. regia_ have been used, and only two of these hybrids have
yielded susceptible seedlings. However, only a few seedlings were
available from certain hybrids.

4. A total of 156 trees of approximately 36 horticultural varieties
has been grown at Beltsville, and only one tree of the variety
Graham has shown well developed symptoms of the bunch disease. Two
other Graham trees have shown slight or questionable symptoms of
the disease.

It should be pointed out that a considerable number of heartnut and
butternut trees were planted at random in the same orchards with the
black walnut trees used in these experiments and at the same time
(1932). In many cases black walnut trees grew within 50 or 100 feet of
the heartnut trees. The bunch disease first appeared on heartnut trees,
the most susceptible walnut species, and spread quickly to butternut,
which is also very susceptible. By 1940 most of the diseased heartnuts
had been removed from the orchards, but it was not until after the
top-working experiments described above were completed that the orchards
were cl