Chapter 20
HYBRIDIZING
Working with nature to develop new varieties of trees is fascinating although it requires infinite patience and study combined with skill and concentration. A person without experience may taste of this pleasure, however, by trying his hand at cross-pollination, and there is no end to the number of hybrids possible.
In attempting to make crosses, one must necessarily understand the botanical relationship between the trees to be crossed. Trees of the same species cross readily in almost all cases; trees of the same genus are not as easily crossed; trees belonging only to the same family are usually difficult to cross. It is generally a.s.sumed that trees not in the same family are impossible to hybridize. The plum serves as a practical example of this. The American wild plum crosses readily with almost any other plum and particularly well with the j.a.panese plum.
These crosses have resulted in such phenomenal fruit as the Underwood plum, a cross made between species. If a cross were made between a chestnut and a walnut, it would be between members of different families. I recommend to anyone who is attempting to cross-pollinate for the first time, that he limit his work to crosses made within species.
His chances of success will be greater and such success added to the experience he is acquiring, will give him the background needed for more difficult hybridizing.
Crosses made between filberts and hazels usually produce great changes in the resulting fruit. J. F. Jones won considerable horticultural fame from crosses he made between the wild American hazel known as the Rush hazel, and such varieties of the European filbert as the Italian Red and Daviana. Hazel and filbert cross readily and the resulting seedlings will usually bear after only three or four years. For both these reasons, they are good material for a beginner to work with. If the wild hazel is to be used as the female, or mother, of the cross, it is necessary to pick off all the male blossoms, or staminate blooms. This should be done long before they begin to expand. The pistillate, or female blossoms, should be enclosed in bags, about six of the three-pound, common kraft bags should be enough. These are slipped over those branches which bear female blossoms and are tied around a heavy packing of absorbent cotton, which has been wound around the branch at approximately the place where the opening of the bag will be. In fastening the mouth of the bag around the cotton, I find that No. 18 copper wire, wrapped several times around and the ends twisted together, is more satisfactory than string. This makes a pollen-tight house for the pistillate blossoms but not one so air-tight as to cause any damage to either the plant or blossoms.
In order to have pollen available at the proper time, it is necessary to cut a few filbert branches which bear staminate blooms and store them in a dark, cold place to prevent the pollen from ripening too soon. I recommend keeping such branches in dampened sphagnum moss until it is time for the pollen to ripen, or if a cold cellar is available, burying the cut ends of large branches carrying male catkins one foot deep in clean, moist sand. When the pollen is wanted, the branches should be placed in a container of water and set near a window where sunlight will reach them. Usually, after one day of exposure to bright sunlight, the staminate blooms will expand and begin to shed their pollen. The pollen may easily be collected by allowing an extended catkin to droop inside a vial or test tube and then, as the catkin rests against its inner wall, tapping the outside of the tube sharply with a pencil to jar the pollen grains loose. A separate test tube must be used for each variety of pollen to be experimented with. By following this procedure for several days with all the staminate blooms that have been gathered, the experimenter should have enough pollen for work on a small scale. The test tubes containing this pollen should never be stoppered with corks, but with plugs of absorbent cotton, which will allow the pa.s.sage of air.
Pollen may be stored in this manner for several days, possibly as long as two weeks, if it is kept dry. By a close observation of the blooming period of the wild hazels, one is able to determine the best time for placing the filbert pollen on the pistillate blossoms. No attempt should be made to do so until the male catkins of the wild hazel species are so entirely exhausted that no amount of shaking will release any grains of pollen. When this condition exists, it is time to move the stored filbert branches to strong sunlight. A quiet day should be chosen to pollinize the hazels for two reasons. If there is a wind, it will blow away the pollen and so make the work more difficult. A wind will also increase the danger of the hazels being fertilized by native hazel pollen which may still be circulating in the air and which the flowers may prefer to filbert pollen.
When good conditions are present, then, the hybridizer proceeds to his work. A brush with which to transfer pollen from the vial to the pistillate blossoms is made by wrapping a little absorbent cotton around the end of a match. The paper bag is removed from around a group of hazel blossoms, a small amount of pollen is dabbed on each blossom and the bag is immediately replaced, to remain on for two more weeks. When the bags are finally taken off, the branches should be marked to indicate that the nuts will be hybrids. Before receiving pollen, each pistillate blossom has, emerging from its bud tip, a few delicate red or pink spikes which are sticky enough to make pollen adhere to them.
Within a few days after receiving pollen, these spikes may dry up and turn black, a fair indication that the pollen has been effective. If the pollen does not take hold, the spikes of the staminate blooms are sure to continue pink for a long time. I have seen them in the middle of the summer, still blooming and waiting for pollen which would let them continue on their cycle. This ability of hazel flowers to remain receptive for a long period allows the nut-culturist ample time to accomplish his work. It is not so true with all members of the 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 b.u.t.ternuts and j.a.panese heartnuts. Many of these are of some worth and are being propagated. Crosses between heartnut and b.u.t.ternut 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 gla.s.s vial which does not hold more than an ounce of liquid. An atomizer bulb, attached to a short copper or bra.s.s tube soldered into a metal screw-cap, is fitted to the vial. Another small copper or bra.s.s 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.
[Ill.u.s.tration: _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._]
[Ill.u.s.tration: 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 gla.s.s 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
Although quack gra.s.s will grow luxuriantly up to the trunks of both black walnut and b.u.t.ternut trees, I know, from things I have seen myself, that the roots of the latter and probably of the former have a deadly effect on members of the evergreen family. I have seen northern white pine and other pines, too, suddenly lose their needles and die when, as large trees, they have been transplanted to the vicinity of b.u.t.ternut trees. To save as many of these transplanted trees as possible, it was necessary for me to sacrifice almost one hundred fine b.u.t.ternut trees by cutting them off close to the ground and pruning all the sprouts that started.
Other instances have also demonstrated to me this deleterious power of b.u.t.ternut trees over evergreens. For years, I watched a struggle between a small b.u.t.ternut tree and a large Mugho pine. Gradually the Mugho pine was succ.u.mbing. At last, when the pine had lost over half its branches on the side near the b.u.t.ternut, I decided to take an active part in the fight. I cut off the trunk of the b.u.t.ternut and pruned off all of its sprouts. The b.u.t.ternut surrendered and died. The Mugho pine took new heart, lived and again flourished.
At another time, I transplanted several thousand Montana pines, about thirty or forty of which came within the branch limits of a medium size b.u.t.ternut tree. Within a year, these thirty or more trees had turned brown and were completely dead, while those immediately outside the branch area were dwarfed and not at all thrifty. The trees farther from the b.u.t.ternut were unaffected and grew consistently well. A similar condition, although not to the same degree, developed under a white oak where more Mugho pines were growing. Another instance occurred when a planting of several thousand Colorado blue spruce were lined out and fell within the area affected by two b.u.t.ternut trees. The spruce were all dead within a few months.
Many people have observed the detrimental effect of trees of the walnut family on alfalfa, tomatoes and potatoes, resulting in wilting and dying. It is the root systems of the walnut which are responsible for this damage. Apparently, there is some chemical elaborated near the surface of the roots, and sensitive plants, whose roots come in contact with either roots or ground containing this factor, are injured and sometimes killed by it. One must therefore be very cautious about trusting these trees as protectors of many of the ornamental and garden plants. I am certain, from my own observations, that their influence on evergreens is strongly antagonistic.
On another basis is the a.s.sociation between catalpas and chestnut trees growing adjacent to one another. Constructive symbiosis apparently develops when a young chestnut tree is planted within the radius of the root system of a catalpa. The latter very definitely influences the chestnut tree to grow more vigorously than it otherwise would.
I have recorded my observations of these antagonisms and friendships between trees and plants to show that they are a reality which should be taken into consideration in grouping and transplanting. Such warnings are infrequent because some people may mistake them as condemnations of certain favorite trees. I do not intend them as such, for these plants are often valuable and worthwhile. This ability which they have developed through the many years of their existence is a guarantee of the st.u.r.diness and strength of their family and species, not at all a quality to be condemned.
CONCLUSION
If I had written this book twenty years ago, I would have prophesied a future for nut culture in the north, full of wonder, hope and profit. If I had written it ten years ago, I should have filled it with discouragement and disillusion. Now, after growing such trees for more than 30 years, I realize that the truth lies somewhere between these extremes, but nearer the first.
It is seldom practical to move native trees very far from their natural range, nor is it necessary to do so in this part of the north: We have four fine, native nut trees: the hazel, the b.u.t.ternut, the black walnut and the hickory. In my experience, these four have completely demonstrated their practical worth.
If commercialization is the primary hope of the nut tree planter, he should first consider the large, hardy hybrids, known as hazilberts, which I have produced between a large Wisconsin wild hazel and European filberts. Hazilberts equal the best European filberts in every way, without the latter"s disadvantage of susceptibility to hazel blight and its lack of hardiness. They are as hardy as the common wild hazel and are more adaptable to environment and soil conditions than any other native nut tree. They may be trained into trees or allowed to grow as large bushes. Like all other filberts and hazels, they, too, need companion plants for cross pollinization to obtain full crops of nuts.
The b.u.t.ternut is also a very adaptable tree. No one who is acquainted with it, questions the quality of the b.u.t.ternut kernel. In a good variety, the nuts should crack out in halves and the kernels drop out readily.
So many good varieties of black walnuts are being propagated, I need not say much about them, except that many of the best ones are not practical for this climate. Nurserymen who grow them can give the best advice about varieties to anyone selecting black walnuts for orchard planting.
Hickories are the last of these native trees to be recommended from a commercial standpoint, as they are the most particular about soil and climate. However, with improved propagation methods and planting technique they should become some day as valuable as pecan plantations have become valuable to the south.
Considering the nut tree as a dooryard tree, an ornament rather than a business, makes it possible to include many more species as suitable for growing in the north. For this purpose, I suggest heartnuts, chestnuts, pecans and hiccans. The heartnut tree is always one to draw attention and interest, picturesque in its leaves, blossoms and cl.u.s.ters of nuts.
Last, but certainly not least in it potentialities, is the English walnut. I am certain that we shall have some varieties of these which will be hardy enough to plant in the north. When these have been completely proven, they will be a delightful addition to the number of trees flourishing here. What family would not receive enjoyment and satisfaction from having, in its dooryard, a gracious English walnut tree, its spreading branches laden with nuts?
Although the commercial aspect of producing hazilberts is engrossing me at the present time, my greatest pleasure in nut culture still comes, as it always shall come, from actual work with these trees. It is both a physical and mental tonic. I recommend nut tree culture to everyone who enjoys spending his time out-of-doors, who is inspired by work of a creative nature, and who appreciates having trees, or even one tree, of his own. Suggested reading on Nut Tree Culture:
Nut Growing by Morris Nut Growers" Handbook by Bush Tree Crops by J. Russell Smith The Nut Culturist by Fuller Improved Nut Tree of North America by Clarence Reed Annual Reports of N.N.G.A.