Robert T. Morris, New York
At the present time when our views on the subject of top working trees are based upon incomplete knowledge and experience perhaps it is unwise to present a paper upon the subject which might be taken as authoritative. On the other hand my experience to date is worth recording for its face value, subject to change of view subsequently.
Different species of hickory act differently when subjected to top working methods. The bitternut may be cut back severely without giving evidence of any great degree of shock. The shagbark on the contrary makes slow recovery and many years are required for a cut-back shagbark hickory to regain normal equilibrium between top and root. The pignut and mockernut apparently stand midway between the bitternut and the shagbark in respect to the trimming of the top. My experience with shagbark includes the top working of trees ranging from a few inches in diameter up to fifteen or twenty inches in diameter, and the cutting back has included all stages from actual felling of the tree to cutting off half of the top or less than half of the top. The idea of felling trees completely was to graft stump sprouts or to insert the slot bark graft into the stump near the ground. When this has been done the larger hickories do not send up stump sprouts at all and the root dies excepting in cases in which a slot bark graft has been introduced. The graft grows slowly without a great degree of vigor and requires so many years for balancing the root that the method has not been practical up to the present time. The same statement is true of the shagbark hickory which has been trimmed back very severely leaving nothing but the stubs of large branches to be grafted immediately or for the purpose of grafting sprouts in the following year. The bark of the shagbark hickory is so hard that new shoots are choked severely and many years are required before they have a secure hold upon the stock. My final conclusion is that we may cut shagbark limbs having a diameter of three inches or less for the purpose of leaving grafting stubs. If a large number of grafts are inserted in such a topworked tree or in stock sprouts which start and are grafted in the following year the work is successful. In order to avoid the labor of topworking a large shagbark tree in its entirety we may graft only one or two limbs and allow stock sprouts to grow on other limbs until both stock sprouts and graft sprouts have become well branched. Branches carrying stock sprouts may then be removed a few at a time year after year, leaving the graft sprouts in charge finally.
By means of the bark slot method of grafting grafts may be inserted in any part of a hickory tree. The bark slot method consists in using a chisel and mallet for cutting parallel lines the width of the scion in the bark of the stock. The tongue of bark between the parallel lines is pried outward with the point of the chisel until the scion has been inserted next the wood and the tongue of bark is then allowed to return to place, leaving the scion interposed between the tongue of bark and the wood. Rules which apply to the shagbark may be applied to all of the hickories with which I have experimented. When cutting back the limbs in preparation for topworking it is well to leave as many as possible of stubs or branches of small diameter. Branches of small diameter may be grafted by ordinary cleft grafting methods but branches of larger diameter should be treated by the bark slot method. At the present time and in the locality of my country place at Stamford, Connecticut, melted paraffin suffices in place of grafting wax and melted paraffin is brushed over the entire scion, buds and all, as well as over the wound in the stock.
The time for cutting back hickories in preparation for topworking is probably important and in my experience to date, autumn cutting is preferable. The reason is that a good deal of activity is going on in the tree before it enters into a state of winter rest and wounds are pretty well repaired. In winter cutting there is some danger of incomplete repair and in the springtime the free flow of sap invites the entrance of various enemies, bacterial and fungous. Summer cutting according to the laws of plant physiology would cause more shock to the tree than cutting at any other time, although practically I have done this successfully. Without regard to season for cutting in preparation for topworking it is very important to trim cut ends very smoothly with a sharp knife in order to remove ragged tissue left by the saw. It is difficult to persuade employees to do this and it will not be done as a rule unless the owner looks after the matter personally. The smoothly trimmed end of the cut branch should immediately be protected with white paint, melted paraffin, or some other protective covering.
What are the disadvantages of the slot bark method of topworking hickories? The scion does not have such a secure hold upon the stock as it does in cleft grafting and it will blow out in a high wind unless it is protected by braces. I have found it not harmful to a tree to fasten laths to the stock for holding the growing scion, driving galvanized iron nails through the lath directly into the stock. Unless growing grafts are well braced by some method the entire season's work may be lost in two minutes of a gale preceding a thunderstorm in summer. By the slot bark method, in other words, we may catch more grafts and lose more grafts than by any other method with which I am familiar, but the loss may be avoided by proper attention.
The best time for grafting varies with the locality. At Stamford I have grafted hickories from February until September. Very early grafting is largely a failure because of incomplete repair of the wound in the stock and scion. Late summer grafting is not practical because the scions which make a start do not lignify their new shoots sufficiently to withstand the winter cold. In late April or early May when the sap is running very freely we also have a considerable loss of scions because an excess of water causes the scion shoots to grow too rapidly before wound repair has taken place to the point necessary for conducting nutrition for the growing shoots. Grafting after the leaves are pretty well out on the tree has given me best success. Grafting from then up to the last week in July has been found to be practical. Scions for topworking hickories have been employed for what I call "mediate" and "immediate" grafting. By mediate grafting is meant the employment of scions which have been cut while they were dormant and which have been stored in any appropriate way. Immediate grafting means the transference of scions cut from one tree and used upon another in the same hour or day. Mediate grafting is the sort which belongs to all history of the subject and immediate grafting relates more particularly to my recent experimental work.
Mr. Bechtel: What kind of wax did you use if any besides paraffin?
Dr. Morris: I have given up everything but that. The paraffin has a number of special advantages. In the first place, it seals any wound against infection from bacteria or fungi. It prevents moisture from rain carrying bacteria into the wound. It prevents evaporation from the cut surfaces.