GRAFTING AND BUDDING
SHORTCUTS TO QUICK TESTS
Nowadays we hear of some remarkable experiments in the grafting of animal tissues, which strongly appeal to those who have long experimented in the grafting of vegetable tissues. The experiments made by Dr. Alexis Carrel, of the Rockefeller Institute in New York, are of particular interest. It appears that Dr. Carrel has devised a new method of suturing arteries. With such a process, the plant experimenter of course has no concern, for the juices of plants are not transmitted in any such definite channels as the arteries and veins of animals. But in dealing with animal life the arteries are all essential, and the process devised by Dr. Carrel enabled him to perform grafting experiments such as no physiologist or surgeon had heretofore found feasible. Not only did Dr. Carrel transfer sections of arteries from one cat or dog to another animal of the same species; but he also transplanted successfully even such vital organs as the kidneys. Moreover, what is more spectacular even if not more important, he actually succeeded in amputating the leg of one dog and grafting it on the amputated stump of the leg of another. The transplanted limb presently made union with its new stock, as a horticulturist would term it, and the borrowed member became a permanent portion of a new body, just as the cions of my apple trees or plums become component parts of the tree on which they are grafted. All this, as I said, was so fully in keeping with the familiar experience of the plant experimenter that it had no peculiar interest for me. Perhaps it seemed to me less wonderful than it really is because my conception of the fundamental unity of plant and animal life makes it appear to me inherently plausible that such transplantation of members should take place under proper surgical conditions. The only difference is that the method of grafting plant tissues one upon another has long been familiar, whereas no one knew just how such grafting could be accomplished in the case of the animal until Dr. Carrel found the way. But I think what interested me most about Dr. Carrel's experiments was the demonstration his tests made of the limits of successful grafting where the organs or members involved belonged to different species. For, whereas he found that the kidneys and spleen might be transplanted from dog to dog, or from cat to cat, it was quite out of the question to hope for a successful issue if he transferred one of these organs from cat to dog or from dog to cat. Even when the transplanted tissue consisted merely of a piece of artery, it was found that the graft did not take kindly to its new surroundings, unless the animal were of the same species as that from which the artery was taken. Something inherent in the chemical composition of the tissues themselves makes every fiber of the tissue of a cat, seemingly, more or less antagonistic to the tissues of the dog. We have already seen how the experiments of Dr. Nuttall, of Cambridge University, demonstrated that the quality of felineness or canineness, so to speak, penetrates to the last drop of the blood; so it is not surprising to find from this independent source that the same characteristic differences extend to the solid tissues. And of course I am at once reminded of the similarity of experiences of the grafter of plants. Here also there are sharp limits fixed to the feasibility of the grafting method. You may transfer the twig of an apple to the corresponding limb of another apple tree, however widely different, with entire facility. You may similarly, although with far less facility, make a graft between twigs of the apple and the pear. In the same way you may combine branches of the different members of the family of stone fruits-plum with apricot, peach with almonds, and the like. But if you attempt to ignore the larger barriers, and strive to graft seed fruit upon stone fruit-apple or pear on plum or peach-your effort will result in failure, just as Dr. Carrel's experiments resulted in failure when he attempted to transpose the organs of cat and dog. It would be interesting if Dr. Carrel were to extend his experiments so as to test the possibilities of transposing the organs of different species within a family-say from wolf or fox to the dog, or from lynx or leopard to the cat. Here, to judge from our experiments with plants, the probability of success would be far greater. At all events, we are commonly able to make such grafts as we choose between different species of the same plant genus; and we may reasonably infer that the same thing might be possible in the case of animals. It has also been found that in plant life where there has been much crossing either naturally or by intent in the past that most striking individual differences appear. Some individual seedlings among any lot of such crossbred plants (all of which may have come from the seeds of a single variety), will thrive when grafted on certain other species or varieties even better than on their own roots, while other individual varieties refuse to combine or grow under any conditions; for instances, the common French prune thrives better on almond roots than on its own, the golden drop plum will not live when grafted on the peach while some of its nearest relatives, the common French prune and others, grow, thrive and produce fruit abundantly. It thus appears that artificially produced varieties may acquire really specific difference of a profound nature.
THE MUTUAL INFLUENCE OF CION AND STOCK
Leaving the solution of this problem to the physiologist, however, let us turn to the specific task in hand, and consider that very important part of the plant experimenter's task that has to do with the grafting of vegetable tissues. It is convenient to recall that the trunk or branch upon which a twig is grafted is called the stock, and that the transplanted twig itself is spoken of as the cion. The practical methods of grafting, as applied to different varieties of plants, will be detailed in a moment. But first I wish to consider very briefly the mutual influence that cion and stock exert upon each other. That there is an intimate chemical and vital relation between the immediate living surfaces of stock and cion admits of no question. The very fact that we cannot cause plant tissues to make union unless they are of allied species, is in itself sufficient proof of this. Moreover, the fact that the cion must receive its entire supply of water, conveying all nourishment except carbon (which is drawn from the air) through the medium of the tissues of the stock, suggests that there must be a uniformity of chemical composition between the two that might be supposed to amount almost to identity; particularly after the cion has been in place for a term of years, and has grown from a tiny twig to a large limb. Yet, in point of fact, there is abundant evidence that the cion maintains its original identitY of character from first to last. This may be more readily understood when we know that all plant food is developed within the foliage. To be sure the roots supply water, the universal solvent and transportation agent of all life, and small quantities of certain minerals and organic substances in solution, but these are not digested for assimilation as plant food until combined with carbon dioxide which is transformed in the leaf cells under the influence of the active rays of light, first into fruit sugars and by later transformation to cane sugar but oftener to starch, a more stable form of food substance, in which form it is most commonly stored in seeds, bulbs, tubers or enlarged roots or stems, or to wood and less often to various other substances used in the economy of plant life and quite often useful to animal life and to the industrial life of man. These transformations are presented to us in the various food products and the numerous gums, rubber, coloring materials, drugs, oils, and perfumes. Thus it will be seen that every organic structure on the earth, every plant and animal whether of earth, sea or air, including man himself, is wholly dependent upon the food always first developed in the leaves of the plants. But to return to our cions-a twig of the Baldwin apple, grafted on a wild crab apple tree, will produce Baldwin apples, and not wild crab apples. Moreover, the Baldwin apples thus grown will be identical in appearance and flavor with those that grow on the tree from which the cion was cut. This seems very mysterious, but the like of it is matter of every day observation in the orchard of the up-to-date fruit-grower. Nevertheless, the question has more than once arisen as to whether cion and stock may not exert upon each other an influence of a profoundly modifying character. That such may be the case, to the extent of producing a poisonous influence, has been observed in the case of grafts between species somewhat distantly related. It has been observed, for example, that some of the English plums unite with the peach, and do fairly well for a time, while others refuse to unite under any circumstances, and still others when budded or grafted on a peach stock seem to poison the peach tree, even causing its death. Yet, on the other hand, the French prune will often grow better on the roots of the almond or the peach than on its own roots. In each of these cases, it would seem, there must be an influence, in one case harmful, in the other beneficial, transmitted between cion and stock. It will be observed that such influences as these merely extend to the life or vigor of the plant, and have nothing to do with the question of transferring its inherent characteristics. And it is universally admitted, that, as a rule, the influence of stock on cion, or of cion on stock, is thus limited. A cion of tender race may thrive on the roots of a hardy stock, for the simple reason that these roots have vigorous growth and large capacity for imbibition of nourishment. But just as you cannot make a dog and cat identical in constitution merely by feeding them the same food, so you cannot cause a grafted cion on your peach or pear or apple tree to conform in shape or constitution to the stock on which it grows merely by giving it the same nourishment that the stock receives-for as explained above all the most important functions of plant life are carried on in the leaves. Thus we may have an explanation of the fact that the graft governs the root almost absolutely as to variety or individuality, while the roots are purveyors for the foliage.
Nevertheless, I have had at least one experience in the course of years of practice in grafting that seems to demonstrate the possibility of the transfer from cion to stock of qualities that transform in a very tangible degree the essential characteristics of the plant. I refer to a case in which the twig of a purples leaved plum that I received from France was grafted on an old Kelsey plum tree which stood just at the corner of the vine-covered cottage on my old place in Santa Rosa. The graft was made in the season of 1893. I was exceedingly anxious to hybridize this new and interesting importation with some of my plums, so I watched it carefully. But much to my disappointment, no blossom or signs of blossom appeared during the year. So there was no possibility of making such a hybridizing experiment as I desired. Imagine then my astonishment when from a quantity of seeds gathered from the Kelsey tree, there grew next season, among other seedlings, one with deep purple leaves. This strange seedling proved to be a thoroughly well-balanced cross between the original purple-leaved graft that I had imported and the Kelsey upon which the graft was growing. There was a most perfect balance in foliage, fruit, and growth so far as I could judge. The tree wvas light purple in foliage throughout the season. Its fruit was small, nearly globular, and purple in color even when only half grown. Everything about the appearance of this strange seedling seemed to suggest that it was a cross between the purple-leaved plum I had imported and the Kelsey. There was no other purple-leaved plum within thousands of miles. My cion had not bloomed, and so crossing could not have occurred in the ordinary way. So I can see no escape from the conclusion that this was a case of so-called sap-hybridism, the very existence of which has been doubted. The purple-leaved cion had seemingly influenced its host in such a way as to produce what was to all intents and purposes a hybrid progeny. The new purple-leaved seedling was grafted upon an old tree, and in due course I produced several thousand second and third generation offspring from the original seedling. The fruit is of a characteristic red color, and in flavor it closely resembles the fruit that the original purple- leaved cion subsequently bore. In size the fruit is intermediate between that of the purple-leaved cion and that of the Kelsey. The descendants of this hybrid stock vary in the second and succeeding generations, just as they might be expected to do had they grown from a hybrid seed produced by pollenation; thus affording additional evidence that we have to do with an actual case of sap-hybridism.
GRAFTING TO SAVE SPACE AND TIME
I record this case thus at length because of its extreme unusualness. Never in the entire course of my wide experience have I seen another case in which I could trace such definite influence between the grafted cion and its foster parent. And so we may take it as a safe general rule that a cion, however grafted, will retain the characteristics of its parent stock, and that the tree on which it grows will be fundamentally uninfluenced, so far as the character of its fruit is concerned, by the intruder. It is not at all with the expectation of influencing the fruit product of either cion or stock that the familiar process of grafting is resorted to. The chief object of grafting, as practiced in my orchard, is to economize space and save time. As to the former point, it will be obvious that where scores or hundreds of twigs from different seedlings are grafted on limbs of a single tree, we are enabled to watch developments among these hundred of specimens, and by uprooting the original seedlings to utilize the ground they occupy for other purposes. As to time saving, I have discovered that by grafting small cions near the tip of the limbs of the foster parent, instead of near its trunk, the cion comes much earlier to maturity, and bears fruit in the second season instead of waiting until the third or fourth, as it otherwise would do. So it is that on a single tree in my orchard almost a thousand different seedlings may be tested simultaneously; and by the practice of selection of early-bearing varieties during the past thirty years, I have produced seedlings of a type which almost invariably bear the second year from my grafting. Indeed, so universal is this, that not one unfruited cion in a thousand will be saved for the third year unless it possesses some remarkable quality of growth, or shows peculiarly prominent and rounded buds, associated with the broad foliage that betokens unusual possibilities of future fruit-bearing. The reader who has followed the accounts of the long series of experiments necessary to develop say an early-bearing cherry or a stoneless plum will appreciate in some measure the value of a system of grafting which shortens by two or three years the interval between successive generations. It will be readily comprehensible that by the use of these grafting methods I have been able to attain success in development of new varieties of fruits in half the term of years that would otherwise have been required.
GENERAL PRINCIPLES OF GRAFTING
The single principle that underlies all successful grafting, is that the layer of tissue called the cambium layer, lying just beneath the bark of the twig, shall be brought in intimate contact with the corresponding layer of tissue of the stock on which it is grafted. The life-giving sap flows through this thin layer of tissue only. As to the central woody tissues-the so-called heart of the twig-there will be no union between stock and cion in any case. But this is of no consequence since the new growth of wood soon covers the trivial wound with which the cambium layer will make ready union under favorable circumstances; and the growth will continue outward, year by year, until ultimately the cion and stock are so firmly joined that they constitute a branch scarcely less strong than the ungrafted branches of the tree. But unless the living tissues of the cambium layer are accurately joined, no union can take place, and the graft will be a failure. If this essential principle is borne in mind, the process of grafting becomes a comparatively simple one, and one that may be carried out successfully by amateurs with very little preliminary practice. A few specific hints as to the details of the method may, however, be of service. So I shall give a brief account of the methods employed in my orchards, where the process of grafting is carried out thousands of times each year. Grafting may be divided under three headings: (1) Grafting proper, in which a cion or small shoot is inserted into or upon the stock; (2) Marching, in which the cion is left attached to its parent stock until union with the new stock is completed; (3) Budding, which consists of the insertion of a single bud upon the cambium layer of the stock. There is no fundamental difference between the three processes; they are merely different methods of accomplishing the same purpose. Grafting may be more or less successfully carried on at any time of the year. But during the spring and early summer months the vital cambium zone is usually at the maximum of activity, forming wood tissue from its inner surface, and bark from its outer surface. At this time of maximum growth, wounds are rapidly healed, and union between a cion and stock is most rapidly secured. Nurserymen and fruit growers take advantage of this fact. The most satisfactory results almost always follow spring grafting or summer budding. It is necessary, however, that there should be activity enough in the sap movement to form the cellular connection between the stock and the bud before the latter perishes from drying out; sap flow is also necessary to allow the bark to be lifted readily from the cambium for the insertion of buds. The best success usually follows the grafting of mature, or nearly mature, buds in the case of trees and shrubs; though young tender buds often thrive nearly as well.
THE MORE COMMON METHODS
The best and quickest way to graft young seedlings is by "side" grafting. This graft is made by taking a piece of the new wood from the tree to be multiplied, about 21‡2 inches long with well formed buds on it. Slice off both sides of the lower end of the graft in the form of a sloping wedge, the cut on each side being not much over one inch long. Both sides should be alike, but one of the edges should be thicker than the other. The tree to be grafted is bent to one side with the left hand. With the right hand a sloping gash is made downward on one side of the tree just above the ground, and the graft, described above, is pushed down into this cut as far as it will go. The cambium layers of the cion and seedling meet at some point, and a union of the tree is formed. After the cion has been placed, the tree is allowed to spring back to its upright position, and is at once cut off with a pair of pruning shears, about two inches above the graft. Warm wax is often applied with a small paint brush over the wound to keep out the water, germs, and dry air, though waxing is often omitted with good success if the graft is well covered with earth leaving a single bud above the surface. In grafting cions on the branches of trees, as in transforming large trees or whole orchards, the so-called "cleft" graft is usually employed. In preparing for this, the branch of the stock tree is sawed off at a convenient place, the exact position being determined by the character of the experiment. If we are seeking to make a permanent tree, the graft is implanted upon the limb not more than a foot or two from the trunk. But where it is intended merely to test the cion as to its fruiting possibilities, time being an object, it is placed far out among the smaller branches by what is called the "tongue," or "whip," graft. In sawing limbs over an inch thick to serve as stocks, care must be exercised that the limb does not split. In order to avoid this, saw part way through from the top, and finish it by sawing from the bottom. Most persons who graft do not trim the stock after it has been cut, but I have found that the cambium layers join much more readily if the top of the stock is trimmed carefully with a knife so that it is smooth all around the edges. Clean incisions heal best with vegetable just as with animal tissues. In making the "cleft" graft, the stock is split with a grafting tool. The wedge shaped portion of this tool is for the purpose of holding the cleft open until the cions have been inserted. The CiOIIS are then cut and connected with the bark usually one on each side of the cleft. When the tool is removed, the sides of the stock hold the cions tightly so that it is seldom necessary to tie a string or piece of cloth around the graft. It is usually best to put on a piece of cloth, however, after waxing. This insures more uniform results. Grafting wax, a formula for which will be given presently, is usually applied several inches below the crack which was made for the cleft in which to insert the cions. In some cases, however, the stock will later crack below the point where the grafting wax was applied, and when this occurs there is great danger of the graft dying. For this reason it is wise to visit the grafts several times at intervals of a week or so and where any open crack is found, additional wax should be applied. There are various modifications of the cleft graft. One is used for the walnut and fig which it is almost impossible to graft by the common cleft graft. Modifications are made as follows: Instead of splitting the cleft, triangular grooves are made with a fine-toothed saw on several sides of the stock. The edges of these splits are pared smooth with a sharp knife and the cions which are usually large, after being carefully fitted, are driven into these slits with a small mallet. Strong cords are then bound around the stock to help keep the grafts in place until they have united with the stock, when they may be cut to give room for further growth. All cut surfaces should be carefully waxed as in ordinary cleft grafting. It is well to tie ordinary grocery sacks over the grafts, covering the stock as far down as it has been cut. These are allowed to remain until the buds have made a good start when they may be torn open and finally removed. In making all grafts, care must be exercised in getting the cuts on cions and stocks smooth, so that the parts may fit closely together. In the cutting of each side, a single bold clear cut is better than whittling and trimming. The "tongue" or "whip" graft is used in making bench (i. e., indoor) grafts and sometimes in "top grafting" trees. Top grafting consists in placing grafts on the various branches of a tree in order to change it over to the new variety. The tongue graft differs from the cleft graft in that there is a cleft and wedge on both cion and stock. These interlock when closely pressed together as shown in the accompanying picture. This mode of grafting is seldom used except on limbs less than one-half inch in diameter. It is very difficult to make the proper cut on limbs larger than this. In top grafting large trees, it is often well to graft only on the strongest limbs one season, and on the smaller branches the next. In general practice, however, a whole tree is usually grafted over at the same time.
"BARK" GRAFTING AND "INARCHING"
In grafting chestnuts a modified method called "bark" grafting is best. The cion is trimmed very thin and quite a space is allowed for the cambium layer to come into contact with the cambium layer of the stock. A "T" shaped slit is made in the bark of the stock, cutting through to the cambium layer. The flaps about the vertical slit are turned back, the cion inserted, and the lips of the bark closed over it and bound firmly with a piece of cloth or strong twine to give good support. Grafting wax is applied freely. Such grafts are usually made on a fairly large stock where it would be impracticable to split the stock. As a rule four cions are inserted on one stock, for usually two of these die. If they should all live, two should be cut out, as the grafts do best when there are not more than two on one stock. "Inarching," as already stated, differs from ordinary grafting in that the cion is left upon its original roots until the union is made. The plant from which the cion is to be taken is planted close to the plant that is to serve as the stock. The two are brought together and the bark sliced from a branch of each so that the cambium layers come together. This connection is bound and waxed. After union has taken place, the cion is cut off below the union and the stock is cut off above it, thus leaving the cion on a new stock. This process is only exceptionally used, as it requires too much time and expense, and with most plants is usually no more successful than the simpler methods of grafting.
Mention has been made of grafting wax, as being very generally used to protect cion and stock during the process of healing and union of tissue. After testing many formulas, I selected the following, and no other has been used in my orchard for many years: Eight pounds of common resin and one pound of beeswax or paraffine (either will do if no acid or alkali is present, though beeswax is generally preferred) are mixed with one and a half pounds of raw linseed oil. Boiled oils often contain chemicals injurious to plant life. If the wax is to be used in cold weather, it is better to use only seven and a half pounds of resin and a half pound of beeswax in the mixture, thus giving slightly thinner consistency. The ingredients are slowly heated together until the resin and wax are melted and all thoroughly combined. This composition when partly cooled is poured into pressed tin pans, to make cakes of convenient size for handling. The mixture sticks to the tin with great persistence; but by turning the pan upside down and pouring boiling water over it for a few seconds the wax can be shaken from the pan. These cakes are broken into pieces of convenient size, and in use the wax is kept warm in any convenient dish or pan having a short strong handle. The wax may be heated over a small coal oil stove, and when applied to the grafts should be much warmer than can be borne by the hand, but not hot enough to scald the plant tissues. If heated in a double heater, the outside one containing water, the danger of overheating is lessened. If applied with care with a small paint brush, first around the thick bark of the stock, and later, as the wax on the brush cools, on and about the cuts and open joints, no harm will result. The plan of brushing the hot wax about the grafts instead of applying it by the fingers in the tedious old-fashioned way, saves nine-tenths of one's time, and does far better work than could ever be done by the old method. If the wax should prove to be too soft and sticky, as is sometimes the case in very warm weather, melt it over again with more resin added. If too brittle, add a little more linseed oil so as to bring it to the right consistency to spread well, and at the same time "set" well on cooling. It gives the most satisfactory results when about the consistency of ordinary chewing gum. Properly applied, the wax serves as a valuable protective and germ-excluding dressing, comparable in its function to the aseptic dressing applied by the surgeon to wounds or after operations.
MULTIPLICATION BY BUDDING
There is one form of grafting which differs so radically from other methods that it is often thought of and spoken of as if it were a totally different method. This is "budding"; that is to say, the process of transplanting a single bud from one tree to another. This is really only a special case of grafting; it differs from other methods only in that in ordinary grafting the cion usually has several buds instead of a single one. As a practical procedure, therefore, budding has the advantage of supplying several graft from what by the other method would be on'y a single cion. Therefore budding is generally used for the production of nursery stock on a large scale, or for the introduction of rare varieties, grafting material for which is costly or difficult to secure. The method of budding is closely similar to the method of "bark" grafting, already described, except as to season-which, for budding, is June, July, and August, while the trees are in full leaf. A piece of bark about an inch and a half long, with a well-ripened bud, is sliced from a twig of the variety desired, the incision being just deep enough to include the cambium layer and perhaps a minute portion of wood. The bark of the stock is slit horizontally and vertically to form a T; the size of the slits being determined by the size of the bud to be inserted. The upper corners of the vertical slit are gently lifted with a knife and turned back to reveal the cambium layer. The bud is pushed under the bark; the flaps of which are brought over it, and securely tied. Waxing is not usually necessary. In ten to fourteen days, the bud becomes united to the seedling and the binding cord may be loosened or removed. The bud remains dormant, until the next spring. When the leaves begin to start, the tops of the seedlings are cut down to within two or three inches of the bud, all buds being at the same time removed except the one inserted the season before. Thus the vigor of the tree is thrown into the new bud, and by fall we usually have wvell branched trees from 3 to 6 feet high, according to soil and climate, from the single bud which was placed in the seedling the preceding summer. Sometimes instead of allowing the buds to remain dormant over winter they are placed on the young seedling trees earlier in the season. Fully ripened buds for such transplantation may often be obtained in June or early in July. After the bud is inserted, the tops of the young trees are at once broken over at about half their height, leaving only a piece of bark and a part of the wood to continue circulation. If the whole top is removed the result is failure. When the weather is moist or where irrigation is practiced, the buds will often start out even before they are fully united with the stock, though there is a great difference in this respect. Some varieties of hybrid Japan plums and even the common French prune often make 3 to 6 feet of growth the same season. These are called June buds by nurserymen. When well grown they are excellent trees, as they can be transplanted, leaving the whole root system complete, whereas with trees two years old, some of the roots have to be destroyed in transplanting. Another great advantage in the June bud or yearling over the larger two year old trees, especially in California, is that the tops can be cut down low to form heads of any uniform height desired because all the side buds are young and fresh.
HINTS AS TO HEADING AND CULTURE
With most fruit and ornamental trees, the stocks are secured by planting seed. These are planted during the winter in California, and during the fall or early spring in the colder Eastern states. In general practice, seedlings of pears, cherries, apples, etc., of one year's growth are purchased by nurserymen. These are purchased from persons who make a specialty of producing seedling stocks in large quantities. A large portion of these are imported from France, though American seedlings are being more and more used. These young seedlings are lined out in rows for field culture about four feet apart, being planted from six to twelve inches apart in the rows. During the summer following, usually in July or August for cherries, plums, and peaches, and in September for apples and pears, budding or grafting may be done to best advantage. If there is a marked difference in rate of growth of cion and stock, or if for any reason the two do not blend to advantage, an ugly swelling often results at the point of union; hence the experienced grower avoids making such combinations. These plant affinities cannot be foretold; they can be determined only by experiment. As already pointed out, the success, vitality, and growth of a graft will very largely depend upon the affinity between cion and stock. Occasionally species from different genera may be satisfactorily grafted. For example, some of the pears often thrive even better for a time and produce superior fruit wh6n transferred to a Hawthorn or apple stock. Almond cions thrive well on peach or plum seedlings. Apricot cions grow and thrive well on seedling plum or peach stocks. Cherry cions do well on seedling stocks of the wild Mazzard cherry of Europe. The Mahaleb cherry is sometimes used when it is desired to have dwarf-growing trees. The peach generally thrives on its own roots only. Apples thrive best on their own roots or on various wild crab apple oots. Pear cions do well on seedlings of wild or inferior varieties of pears. Most of the seedlings grown in this country are grown from seeds secured from Europe. Quince stocks are sometimes used for certain varieties of pears, more especially for dwarfing and bringing into early bearing. Seedlings of the hardiest and most vigorous growing varieties of plums, either European or American, may be used for plum stocks. The myrobalan plum from France is a favorite. The peach is also used for some varieties. Stocks or the seeds from which to grow them can usually be secured from wholesale growers and dealers. If it is desired to test the qualities of hundreds or thousands of seedling fruits, a knowledge of grafting is of the utmost importance, as several hundred varieties may be readily tested on a single tree. On the Gold Ridge Farm there are single acres on which ripen several thousand distinct varieties of hybrid seedling plums that could not properly be tested one each on a separate tree on less than about seven hundred acres of land. Besides, a seedling grafted into a bearing tree usually produces fruit in two or three years, but if the same seedling were planted as usual and allowed to fruit, it might require five, ten, or fifteen years. There is still another advantage in grafting many seedlings in a single tree; a better opportunity is afforded for comparative tests; if scattered over a large orchard, some trees might be in better condition, or have better roots or better soil than others, and thus no accurate comparative test could be made. In grafting for the purpose of testing seedlings, the weaker-growing seedlings are placed on the strongest-growing branches of the tree, the stronger growers being placed toward the outside and lower down on the tree and on the smaller branches. When so many varieties are grafted on a single tree, some may be extremely vigorous growers, others only moderately so, and still others will be weak, slow growers. In the winter pruning we always take pains to give the weaker growers plenty of space to develop, while the stronger growers are severely pruned. It is no small matter to prune properly a tree on which several hundred varieties are being tested. An ordinary pruner might ruin the tree in a few minutes, by leaving the most worthless varieties almost covering the tree, while smaller, slower-growing varieties of great value might be so crowded that they would either die or become stunted and bear no fruit. This later aspect of the process of grafting, then, is one that imperatively demands the attention of the plant-developer himself, or of his most skilful assistants.
This text is from: Luther Burbank: his methods and discoveries and their practical application. Volume 3 Chapter 5