When I was a boy, the only hickory nuts of any sort available, were those collected from wild trees. The popular boy was one who knew of some trees which furnished the best nuts and who did not keep the news to himself. The squirrels knew the best nuts as well as the boys did and they would go past many hickory trees along fences and groves in order to congregate in the ones which had the nuts with the thinnest shells and plumpest meats of best quality. In the early morning hours I have seen several squirrels in one particularly good hickory nut tree and not a single squirrel in a tree completely filled with nuts, though its branches touches those of the first one. Men are quite as intelligent as squirrels in some respects. Here and there attempts were made at propagating fine hickory trees of various species by planting nuts. It was not generally known at that time that the hickories were so thoroughly crossed like the apples, that they would not reproduce true to type from seed. Attempts were then made at grafting which were mostly failures for many years. We are now on the verge of a great development in hybridization or crossing of choice kinds of hickories and in determining upon which stocks the different kinds of selected hickories may be grown to best advantage. Hybrids between varieties of hickories occur frequently in nature and hybrids between species of hickories occur occasionally. A number of these accidental hybrids have been discovered and some of them are now being propagated. For the most part they do not represent the best quality of the best parent but it is a notable fact that the bitterness of kinds with the bitter pellicle appears to be a recessive character and disappears usually from hybrids between species in which one parent has a bitter nut. Unfortunately, the finer extractive which give character to the nut of the better parent are prone to disappear also. This is in line with our experience in mixing of characters along Mendelian lines. Given a sufficient number of hybrids and we shall have here and there one with spectacular characteristics of special value.
Now that horticulturists at the present moment are turning so freely toward the idea of producing quantities of hybrids artificially, the next generation will see hickory nuts which were not dreamed of in the days when I was a boy. The crossing of hickories is not difficult work. We simply remove the male flowers from branches carrying female flowers before the male flowers have begun to shed their pollen. The female flowers are then covered with oiled paper bags tied over them for protection and when the danger from self pollination has passed, we take off the bags and add a little pollen which we have kept for the purpose—pollen from some trees bearing remarkably valuable nuts.
Nuts resulting from this cross pollination when planted, give us new varieties of trees which never have been seen before by anybody and that is so interesting that very many people will probably take up hybridization as an incident in recreation. Some of the hybrids will bear very early in their history and others very late. If one is impatient to determine at once which ones are to be valuable, he can hurry the process by grafting a number of cuttings from young seedling trees into the tops of larger trees which are already bearing—labeling each graft, so that he may keep track of the seedling stock from which it came. It is possible to put one hundred or more seedlings in the top of some stock tree at one time.
One reason for delay in propagation by grafting is because the hickories like many other trees are slow in making repair of wounds. Grafts usually perished before being accepted by the stock under grafting methods that were in common use. The best step forward in grafting method for hickories is one that I obtained from Mr. J. F. Jones, Lancaster, Pennsylvania. He tells me that he obtained the method from its originator, Mr. E. A. Riehl, Godfrey, Illinois. This consisted in covering the entire graft, buds and all, with melted grafting wax and including also all of the wound and wrapping of the stock. The buds make their way through this grafting wax without any difficulty, but the grafting wax used by Mr. Jones contained lamp black and that used by Mr. Riehl consisted of a beeswax and rosin mixture. It was found that these seemed to be applicable in the North but not farther south in the hotter sun. Examining into the reasons for this, it seemed to me that in all probability the black grafting wax used by Mr. Jones and the brown or amber grafting wax used by Mr. Riehl, would naturally allow the heat rays of the sun to pass through to the graft while halting the actinic ray of light. The latter is extremely valuable for promoting the activity of chlorophyl, which acts only in the presence of light and in the best way in the best light. The heat rays might have certain destructive qualities. With this theoretical idea of the situation in mind, I employed melted paraffin in place of the grafting wax, covering the scions completely as well as the wound in the stock and the wrappings. This immediately proved to be a success. In fact, it appears to have changed the entire subject of grafting nut trees in such a way that any intelligent boy employing this method can now do better hickory nut grafting than would have been possible at the hands of an expert two years ago. The melted paraffin fills the interstices in which sap might collect and ferment, but at the same time, hardening so quickly that it does not introduce the danger of extension between points of contact with scion and stock. The second point of value consists in allowing the actinic ray in the sunlight to act upon the chlorophyl in bud and bark of the scion and it does not attract the destructive heat ray. This is perhaps the most important single point of value and due to the transparency of the paraffin. Third, the paraffin coating, impervious to air, maintains the sap tension equally in the course of fluctuation between negative and positive pressures occurring between night and day, and under varying conditions of light and temperature. This maintenance of equalised sap tension, I believe to be important. The paraffin is waterproof and prevents evaporation from the scion, which otherwise is prone to dry out before granulation of the wound has taken place in the hickories, as in other species which callus slowly. Fifth, under the paraffin coating of stock and scion, the plant apparently does not have that anxiety which would otherwise lead it to introduce the protective feature of superization, the spreading of a corky layer over the wound surface between stock and scion, thus introducing a mechanical obstacle to union.
This method of grafting has extended the grafting season for nearly two months, apparently. Formerly, I hurried to get all of the grafts in while buds were bursting, in early May. During the season of 1919 I grafted hickories up to August sixth experimentally. The last grafts which caught well in a practical way were put in on July twenty-first. After that the proportion of catches was small and the growth feeble. Incidentally, it may be remarked that filberts grafted as late as August sixth, did perfectly well. The scions employed were cut in late winter and kept in the sawdust of my icehouse. I formerly supposed that ice beneath the sawdust was important, but this year I could not get ice and the scions kept just as well. In July, experiments were tried with grafting directly from one tree to another, using wood of the season's growth. This worked well with hazels, but not with hickories or walnuts, only one out of many hickory grafts catching. That one, however, is significant and I hope to work out principles which will allow of direct grafting of hickories as readily as may be done with the hazels.
When a hickory graft is to be inserted into a small stock or branch, the ordinary cleft graft does well. In stock recipients much larger than the graft a side cleft of the width of the scion only is desirable, or better yet the "split bark" method devised by Mr. E. A. Riehl. A straight split is made in the bark of the end of the stock, and the graft crowded down into this split so that it remains between bark and wood finally. My own method for large stocks, is what I have called "the slot bark method." This consists in turning down a width of stock bark measuring the same as the scion in width. When the scion has been inserted into this slot so made, the bark is turned up over it again and fastened there. By this method I have put scions in the trunks of trees nearly a foot in diameter and at any chosen point, sometimes several feet below the ends of cut branches. One may cut off the top of a large hickory tree and then peg the trunk full of scions by means of bark slots.
Another important point in hickory propagation work consists in the employment of the Spanish windlass for fastening graft and stock together. The old time wrapping of twine or of raffia had to be released in order to allow growth at the point of union of scion and stock. When cord is used it cuts deeply into the new growth, and raffia, which is placed on flat, will be burst open. In either case new wrapping is required at a precarious time, according to old methods. The Spanish windlass, which is used in surgery for controlling haemorrage, seemed to me to be applicable for fastening scions in place. It consists in a paraffined cord with ends tied in a firm knot but hanging loosely about the graft and wound. A wooden skewer or any small lever, is then inserted into the loose loop of cord and twisted about until the part of the cord about the graft wound is so snug that it holds the scion in place more firmly than it can be held by any other sort of wrapping. In order to prevent the cord from cutting into the bark, two shields of wood or metal an inch in length, are interposed between cord and bark. The lever of the Spanish windlass is fastened with a cord or with a galvanized nail in order to prevent the windlass from unwinding and the whole covered with melted paraffin. This may remain in place for two seasons without change, holding the scion firmly in place all of that time and requiring no attention. The growing stock separates the two shields very much as it might separate two stones in the field and automatically unwinds the Spanish windlass by sheer force, just enough to allow growth without any unloosening of its holding apparatus.
In hickory grafting, much experimental work remains to be done in the choice of stocks for grafts of different species. Almost all of the hickories that have been grafted upon the pecan hickory stock, seem to do pretty well upon that stock, but the converse is not true. The pecan apparently does not do well as a rule when grafted upon other hickory stocks, even upon those of its cousins in the open-bud group. The shagbark hickory, in my experience, has done best upon stocks of the shagbark or mockernut or pignut. A number of years, however, are required in some cases for determining that point. Shagbarks which I have grafted upon bitternuts have sometimes made a remarkably good start. Then at the end of three or four years they begin to slow up, while shagbarks on shagbark stock, starting slowly at first, surpassed the ones on bitternut stock finally.
In the spring of 1919, I topworked two trees standing near together and of about the same size (thirty feet) with Beaver hybrid (a cross between the bitternut and the shagbark). One of the trees was a bitternut and the other a pignut. Almost everyone of the grafts of the Beaver grew thriftily on the bitternut. Those on the pignut stock practically all caught and made short growth and then began to wilt back. Finally, only one shoot remained alive. This very striking object lesson will have bearing in varying degrees in all of our hickory grafting. According to my experience to date, hybrid hickories are grafted more readily than are straight species or varieties. They seem to have lost family pride and seem to take up with any friend offering economic support. In the case just quoted, however, caprice was shown by the Beaver hybrid which took eagerly to a host of the species of one of its parents. It refused to thrive on the pignut which did not represent either one of its parents although that same pignut stock would have been accepted by shagbark scions—the shagbark representing the other parent of the Beaver. This sort of experience throws open the entire subject in such a large way as to show what possibilities of success and failure lie before us in experimental work. The same method of grafting, the paraffin windlass method, was employed for these two trees which were neighbors.
Interesting experimental work is to be done in finding the extent to which different species and varieties of hickories may be grown out of their indigenous range. At Stamford, the bitter pecan from Texas, appears to be perfectly hardy but it makes very slow growth—sometimes less than an inch in a year. The Buckley hickory also from Texas, grows thriftly at Stamford and so does the Carolina hickory Pecans from the northern belt thrive at Merribrooke, but those from the southern belt have such a long growing season, that their new wood is not yet sufficiently well lignified to stand the winter well. Some of them pull through a mild winter in fairly good order, but on the whole they do not thrive.