he nut tree
group, some, such as the English walnuts, being receptive for such a
short period that only by very frequent examination and many
applications of pollen can one be sure of making a cross.

Early in the fall, the hybrid nuts should be enclosed in a wire screen
to prevent mice and squirrels from taking them before they are ripe.
Such wire screens may be used in the form of a bag and fastened around
each branch. When the husks turn brown and dry, the nuts are ripe, and
ready to be gathered and planted. Careful handling of the nuts is
advisable to preserve their viability. They should be planted in an
outdoor bed which has been fully protected against the invasion of
rodents. A screen such as I described for other nut seed is satisfactory
for these hybrid nuts but it need not be as large as that. After the
nuts have sprouted and the plants have grown for one season, they may be
transplanted into a permanent location where they should again be well
protected against mice by a trunk screen, and against rabbits by driving
a stout stake deep into the ground on the south side of the tree and
tying it to the tree. This use of a stake discourages rabbits from
cutting off the tree.

There are innumerable other crosses that can be made as well as those
between hazels and filberts. It is possible, for example, to cross the
English walnut with the black walnut. Many such crosses have been made
although none of them is known to have produced superior nuts. Thousands
of crosses exist between butternuts and Japanese heartnuts. Many of
these are of some worth and are being propagated. Crosses between
heartnut and butternut are easily made, following the same procedure
used in crossing hazels and filberts, except that larger bags are
necessary for covering the female blossoms. Also, these bags should have
a small, celluloid window glued into a convenient place, so that the
progress of the female blossoms toward maturity can be observed.

When hybridizing walnuts, it is necessary to use a pollen gun instead of
removing the bag from around the female blossoms and applying the pollen
with a cotton-covered applicator. Such a pollen gun can be made by using
a glass vial which does not hold more than an ounce of liquid. An
atomizer bulb, attached to a short copper or brass tube soldered into a
metal screw-cap, is fitted to the vial. Another small copper or brass
tube should also be inserted in the screw-cap close to the first one.