Grafting is but a modification of propagation by cuttings. The scion is a cutting of the variety we wish to propagate, which, instead of being committed to the ground to emit its own roots, is placed in contact with tissues of a nature similar to its own, through which it is to form a connection with the roots and the soil. The success of the operation depends upon the formative cell in this instance also, as in the cutting; new cells are formed upon the cut surface, and the intercommunication takes place through them. Hence we have anatomical limits to grafting; there are physiological bounds beyond which we cannot pass, in our combinations of scion and stock. Our success is in the direct ratio of the affinity that exists between them; thus apple grows best on apple, and even among these we find the closest union and the best results, where there is a similarity between the style of growth, and probably in the character of the cells.
We say, as a general rule, that stone fruits must be grafted upon stone fruits, those bearing seeds, upon seed fruit; but there are limits even here which confine us upon one hand, and give us more latitude upon the other. Thus the cherry may be worked upon the wild cherry (Prunus Virginiana) but it forms a very poor union; the pear will grow upon the thorn, which has a very different seed, but the union is very imperfect and the tree is short-lived; the apple would appear to be much nearer of kin, since it belongs to the same genus, but though the pear will grow vigorously upon this stock, it is no more permanent than upon the thorn: either of them will answer when grafted low, or in the root, to start the cutting, as the scion may then be considered, and to sustain it until it shall have supplied itself with roots. In top-grafting the pear upon a tree of either species, it is found essential to success, and it conduces to the greater durability of the tree, for some branches of the original stock to be left intact to secure the circulation of the trunk, as the union of the dissimilar cells is so imperfect that it does not furnish sufficient vent for the sap. In the case of the cherry we find that the varieties appear to have a greater affinity for those of their own race; thus the Dukes and Morellos do well when grafted upon the Morello stocks, whereas the Hearts and Bigarreau sorts do not make a good union upon these stocks, but prefer the Mazzard, which has a freer growth more like their own. Most varieties will do well upon the Mahaleb stock, which is used as a means of dwarfing this fruit, though not a dwarf. Upon the wild cherry, which belongs to quite a different section of the genus, the cultivated varieties will grow, but they form a very imperfect union.
The peach may be worked upon the plum stock, and is claimed to be somewhat dwarfed by it, and to produce superior fruit. This stock is more congenial to the apricot, which is frequently propagated upon it. Both plums and apricots may be worked upon the peach stock, and they will grow very vigorously, as they will upon the wild plum, but they soon over-grow, and are very apt to break off. When either of these species is used as a stock for the plum or apricot, they should be considered merely as a nursing mother, like the apple or thorn to the pear, which may be wanted to help the cutting until it shall be prepared to stand alone, and feed itself from its own roots. In other words, they should be grafted, not budded, into these uncongenial stocks, and the operation should be performed in the collar or below it, in the root, so that the growing scion may be earthed up, and encouraged to furnish itself with a good system of roots of its own. The success will then depend upon the ability of the scion to emit roots freely.
We must never forget that in grafting, we are confined to very narrow limits. Our scion must be of a similar nature with the stock, each must have cells of a similar character, capable of transmitting their nutritious fluids from one to the other. We must recollect likewise, that the parts must be so co-apted that the cells of wood growth shall be brought into as close connection as possible, in both scion and stock; these cells are found in the layer, called the cambium, which is between the wood and the bark. The crude sap from below will often pass from cell to cell, when the elaborated sap of the cells in the scion is wholly unfitted for the formation of wood cells in the stock below it; of course the union in such a case must be very imperfect, and the product of such a grafting will be subject to accident, and will be short-lived, though the result in fruit, while the union continues, may be very precocious, abundant, and of superior flavor.
Natural grafting may often be observed by the student of nature when wandering among his favorites of the sylvan shades. There can be no doubt that the first hint was thus communicated to the early gardeners. In nature we always find the grafting to be inarching, or grafting by approach; two limbs or even two trees approximating closely, have abraded one another, and have afterward united their tissues most firmly together. This is generally a union of two trees of the same variety or species; but such is not always the case; sometimes trees of very dissimilar natures unite in this manner, but when we examine them we find only a dove-tailing, only a mechanical union, but no vital action subsists between them. The ancients give us some fancy sketches of the unions by grafting of very dissimilar trees, and some moderns who have no higher claim to poetry than their romancing, tell us that we may graft the peach upon the Willow and Buttonwood, and form other equally impossible unions.
The different methods of performing the operation of grafting vary with the character and size, and condition of the stocks to be worked; thus we have splice grafting, whip, cleft, saddle, and side grafting with modifications, and also grafting by approach, which is generally called inarching—though sometimes also practiced where we desire to renew the roots of a tree that are unhealthy, or to restore those that have been removed by accident or by the erosion of some rodent animals.
Fig. 7.
Splice Grafting is the simplest process, and is applicable only where the size of the stock and of the scion correspond pretty nearly; the two are cut with a sloping curve, each of which being made at the same angle, will coincide with the other when they are applied together, as represented in the engraving, fig. 7.
Fig. 8.—WHIP GRAFTING.
Whip Grafting is a modification of the above. Each portion is cut in a sloping manner as in the splice grafting, but each is also split with a thin-bladed knife, as represented in fig. 8. The object in this is to give a firmer union to the two portions, and also to present a more extended surface for the effusion of the new cell tissue that is to form the bond of union in cementing them together. In both these methods, but especially in the first, the parts must be held together in co-aptation by some kind of bandage; this is generally composed of grafting wax, spread upon cloth or paper, or even, as now extensively practiced, upon fine thread. Cotton yarn No. 3 is drawn through melted grafting wax, and as it cools, it is wound upon a reel at the other side of the room, whence it is drawn as wanted by the grafter or tyer. Tying or wrapping is always a good precaution, and when the splice or cleft graft is not very close, it becomes necessary; but thousands of grafts will unite equally well where the parts are covered with earth, without any such appliance.
Fig. 9.—DIFFERENT STEPS IN CLEFT GRAFTING. A, SCION PREPARED FOR SETTING. B, THE CLEFT OPENED BY A WEDGE.
C, THE SCION INSERTED. D, SECTION OF STOCK AND SCION TO SHOW THE CO-APTATION OF THE PARTS OF THE TWO.
Fig. 10.—CLEFT GRAFTING WITH
BOTH SCIONS INCLINED INWARD.
Cleft Grafting is generally done when the stock is larger than the scion, and also where the operation is performed at a point above the ground. The stock