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.  The second tube should be bent to a right angle above the stopper and its projecting end filed to a sharp point.  Without removing the bag from around the pistillate blossoms, the hybridizer forces the point of the atomizer through the cotton wadding between bag and branch.  The pollen in the vial is blown through the tube into the bag in a cloud, covering all the enclosed blossoms.  It is advisable to repeat this on several successive days to make certain of reaching the female blossoms during their most receptive period.

[Illustration:  8 x 8 x 8 foot tightly woven sheet of unbleached muslin stretched over mother hazel plant during pollination period in the process of making controlled crosses between it and filbert parents.  Photo by C. Weschcke.]

[Illustration:  THE WESCHCKE POLLEN GUN

Taper end of copper tube ... not absolutely necessary, but it saves pollen.

Long fibre cotton wad wired to intake side of bulb to strain out foreign pollens that may be in atmosphere.

De Vilbiss atomizer bulb.

Pollen grains

Any small glass bottle with a wide mouth and screw cap.

Tubes A and B—­3/16” outside diameter copper tubing can be purchased at any garage.  Solder both tubes to screw cover C.

Drwg by Wm. Kuehn

How to make pollen gun.]

Chapter 21

TOXICITY AMONG TREES AND PLANTS