Grafting , the process in horticulture by which a portion of a plant is made to unite with another plant, whether of the same kind or of another variety or species. The plant upon which the operation is performed is called the stock; the portion inserted in or joined with it the scion or graft. No attempts toward grafting plants on others which do not belong to the same natural order have been successful. Generally speaking, varieties succeed best on varieties, species on species, or species and varieties on allied genera. All our cultivated fruits, for instance, are improved varieties of some original species. Out of thousands of varieties raised from the seeds of some previous excellent variety, it is not likely that any will be precisely like the immediate parent; some few may be equal or superior to it, but the great majority will be inferior. When a new and decidedly valuable variety occurs, it becomes a matter of importance to perpetuate it in as many individual plants as possible, and this, with trees, is usually done by grafting. The trifling effect that the stock has upon the scion enables the poorer varieties to be employed in furnishing the trunk and root to the smaller and younger scion.
A piece of well ripened wood, in the form of a twig of the growth of the previous season having three or four buds upon it, is thus transferred to the poorer kind, and forms a living extrem-ity, which extends itself into branches and forms a new head or top. Fruit trees are grafted on plants of their own kind, called free stocks, or they are grafted upon a related variety or species to accomplish some particular end. Certain stocks induce early fruiting and a dwarfed growth; to dwarf the apple, it is grafted upon the paradise, a distinct variety of apple; the pear is dwarfed by grafting upon the quince. A species of cherry called the mahaleb (prunus mahaleb) is used for dwarfing the cherry, and the sloe and the beach plum for the plum. The peach upon its own roots does not grow well in stiff and cold soils, and for such situations it is worked upon a plum stock. The pear will grow when grafted upon the apple, but the union is short-lived; it is also sometimes grafted upon the thorn and mountain ash, but such unions are a matter of fancy rather than utility; nurserymen use only the stocks we have mentioned.
The raising of stocks is an important part of the nurseryman's business; though a tree may be grafted at almost any age, in nurseries where hundreds of thousands are worked every year the stocks used are as small as practicable. Free stocks for the apple and pear are raised from seeds, while the dwarfing paradise and quince stocks are grown from layers and cuttings. Most of the grafting in nurseries is done indoors in the winter. The stocks, which are a quarter of an inch or more in diameter, are taken up in the autumn and buried in an accessible place; when worked, the root is shortened, the top cut off, and the scion inserted at the "collar," or where root and stem join. The grafted roots are set in boxes of sand and kept in a cellar until they can be planted in spring. The operation is performed with great rapidity, and several mechanical appliances have been devised for facilitating the work. Sometimes pieces of the root are used as stocks, but there has been much discussion and great difference of opinion as to the value of the trees so produced.
Stone fruits are more difficult to graft than the apple and pear, but if it be done sufficiently early in spring the plum may be so treated very successfully; the peach is rarely grafted at the north, but it succeeds at the south; this fruit is usually propagated by that form of grafting called budding. Although fruit trees are grafted with scions of ripened wood, there are some trees which will only succeed when green wood is used for both scion and stock; this kind of grafting is called herbaceous. Many evergreens can be grafted in the ordinary way, but the pines only succeed with herbaceous grafting, and the same may be said of some nut-bearing trees. Ornamental trees of various kinds are propagated by grafting, especially where it is desired to perpetuate some individual peculiarity, such as a pendent or weeping habit, or foliage of an unusual shape or color. Some weeping trees which are naturally low, as the weeping beech, ash, and poplar, form elegant specimens when grafted upon a stock 8 or 10 ft. high. Among ornamental trees and shrubs grafting is resorted to as the most rapid means of propagation: sometimes a variety cannot be multiplied readily from cuttings, but can be grafted upon some related stock that will grow rapidly.
The choicer species of clematis, now so much prized as ornamental climbers, take root with great difficulty, while some of the older kinds strike root freely; the florist grows these from cuttings, and grafts the more difficult subjects upon their roots. The fine double camellias will not grow from cuttings, but are propagated by grafting upon the single kinds which readily do so. Epiphyllums and other trailing cactuses make fine plants by grafting them upon a stout stem of cereus triangularis or one of the pereskias. Successful grafting of the apple upon the maple, the rose upon the black currant, and the like, is impossible, although instances of it are often narrated. - The utility of the operation of grafting depends upon the fact that a bud is the representative of the tree from which it is taken; it has the possibility of unlimited development; and as it will, if allowed to extend into a branch on the tree where it has formed, repeat all the characters of the tree, so when taken from the tree which produced it and planted as it were in the substance of another tree, it will develop a branch like the parent tree, and not like the stock with which it is united.
Between i the wood and bark of exogenous trees, including all northern fruit trees, there is a layer in which the forces of vegetation are most active; here the wood of the tree receives each year a layer of new wood, outside of the old, and the inner bark has deposited upon it a new layer upon the inside of that of previous years. This portion, which is neither perfect wood nor bark, but the place where both are being formed, is called the cambium layer. It is this which, if a cut be made in a tree, sends out a new growth to close over and repair the wound; and it is upon the extraordinary vitality of this cambium that the success of grafting depends. The mechanical operations of grafting are various, but they all have for their object the bringing of the newly forming wood and bark of the seion into the closest possible contact with those of the stock. As a general rule, grafting is most successful when the scions are quite dormant, but the forces of vegetation in the stock are active. Fruit-tree scions are cut at any time after the fall of the leaf before the buds begin to swell, and kept in damp sand or saw dust to prevent drying. - Cleft grafting is in this country the most common and likewise the most clumsy method, and yet very often the most successful.
It is practised upon stocks from an inch to several inches in diameter. The branches of old trees are renewed by this method, the grafts being inserted in the branches. Sometimes the entire tree of four or five inches diameter is cut to a bare stock and used in the same manner. The stock, whether trunk or branch, is cut over horizontally with a sharp saw, and the surface pared smooth with a knife; a cleft about two inches deep is made in the stock with a grafting knife and mallet; the scion to be grafted is prepared by sloping its lower end in the form of a wedge about an inch and a half long, leaving it a little thicker on the outer edge. The cleft being kept open with a wedge, the scion is carefully pushed down to the place fitting its inner bark on one side, so that the inner edges of the bark of stock and scion may coincide. The wedge is then withdrawn, and the scions are retained in place by the springing together of the cleft, when the graft is covered with a mixture of loam and cow dung, or with grafting wax, to exclude the air and to facilitate the union. Until a few years ago clay and loam were exclusively used, but grafting wax is neater and more effective.
Various compositions are in use; they consist of resin and wax melted together, with lard or linseed oil, and should be of such consistency as to remain plastic in cool weather, yet not run in hot weather. It is best applied by means of strips of well worn muslin or calico saturated with the composition. For root grafts, well waxed cotton twine, or paper waxed on one side, may be used. Where the stock is large two scions are put in on opposite sides, but with small stocks only one is used, and the stock at the side opposite to the scion is cut in a sloping manner to facilitate healing. - Another process, called whip or tongue grafting, is considered the most expeditious. The stock upon which it is performed must be slender, from the size of a goose quill to any diameter which coincides with the thickness of the graft. Some smooth, clear part of the stock being selected, it is sloped on one side with a knife to a very acute angle. A scion having two or more buds, and of the size to match the stock, is cut with a slope to correspond with that upon the stock; then upon each slope or cut surface is cut a tongue; the scion and stock are locked together by means of these tongues in a manner that will be understood by an examination of the engraving.
The barks of both being made to correspond, a piece of waxed cloth or waxed twine is wound round them to hold them in place. After the graft pushes its buds, the binding should be loosened and finally removed, when the adhesion is completed. This method is used in root grafting, and may be practised also on flowering shrubs. - In saddle grafting, the scion is cleft instead of the stock; the stock is pared away on each side to an acute angle, so as to allow the scion to sit or ride upon it, and the union of the edges of the barks made as complete as possible on each side. - Crown grafting is by many preferred to cleft grafting, as there is no split made in the stock, which often leads to decay; it is practised upon large trees of which the wood is too hard and stubborn to he cleft, or upon small stocks. Several scions are pared away on one side of the lower end for about two inches, so as to make that side flat and leave a shoulder forming a right angle with it. The head of the stock being sawn off horizontally, and the cut portion smoothed, the bark is gently raised from the wood and thin wedges inserted. The scions are now pushed under the bark, their shoulders resting on the crown of the stock; the wedges being withdrawn, the whole is covered with wax or waxed cloth.
After the grafts have grown, and made long, tender shoots, which they will be apt to do with much rapidity and vigor, they should be secured to long stakes planted near the stock and rising above it, to prevent the wind from breaking off the newly formed top at the junction with the stock; or where the grafts are in the head of a tree, their vigor is controlled by pinching. - Sometimes it is essential to replace limbs that have been broken from young trees, or from branches of older ones, and to restore the symmetry of form; and this is done by side grafting. Here the bark and a little of the wood is sloped off from the side of the trunk or of the branch, and the lower end of the scion is cut so as to fit the part as near as possible; it is then fixed in the branch or trunk, first tonguing both as in whip grafting, tying them with bast, and claying or waxing over. Another form of side grafting is used on the camellia and other hard-wooded shrubs; a long, nearly perpendicular cut is made in the stem, in which the scion is placed. - Inarching is only a kind of grafting, and is employed where the cut scion is not easily united to the desired stock.
Two branches, or two stocks of the two distinct plants, are brought close together, and the prepared surfaces are matched and tongued, as in whip grafting; after a while a perfect union will take place, when the inarched portion is to be separated from its parent root, and it henceforth becomes the branch or top of its new foster mother. The two plants to be inarched must be brought near to one another, which is usually accomplished by having one of them in a pot. In some cases the same object is effected by placing the lower end of the branch to be inarched in a bottle, which is kept supplied with water. - Budding is only a variety of grafting in which a single bud is used instead of a scion with several; it is also called shield grafting. (See Budding.) - The practice of grafting seems to have been long known; but the pro-cesses have multiplied with the discoveries and improvements in horticulture, and others besides those mentioned here are employed for particular subjects. A full account of all the processes known will be found in L'Art de greffer, by Baltet. Du Breuil's "Arboriculture," Barry's "Fruit Garden," and Thomas's "Fruit Culturist" may also be consulted for practical details.
Fig. 1. - Cleft Grafting.
1. The operation with the stock out horizontally. 2. With a sloping cut.
Fig. 2. - Whip Grafting, showing the tongues prepared and after-ward bound together.
Fig. 3 - Whip Grafting on the Collar.
Fig. 4. - Crown Grafting. showing the completed operation and an enlarged view of the scion.