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.
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