1,913
edits
Changes
no edit summary
Grafting, Multiplication by. Grafting is the operation of inserting a part of one plant into another plant or part with the intention that it shall grow and produce its kind.
The practice of grafting, together with all the reasons, consequences and results, constitutes a department of knowledge known as graftage. The term grafting is ordinarily restricted, in popular speech, to propagation by means of short twigs or cions, and budding is used to designate the insertion of single buds that arc severed from the branch on which they grew; but these distinctions are not fundamental. Stock is the plant or part on which the grafting is done. Cion (scion, sion) is the part inserted into the stock, although it is usually restricted to cuttings of twigs, and does not include detached buds. In many writings the word is spelled scion, but the other is shorter and it was a very early horticultural term, many old horticultural writings using don and cyan. Scion is apparently later, and usage is not uniform. The word graft is sometimes used in the sense of don, but it would better be used for the completed thing — the new plant or part made by the joining of cion and stock.
Grafting is not always employed for purposes of propagation. It may be a reparative process. What is known as bridge-grafting is of this kind. Wounds or girdles may be bridged by cions, as in Fig. 1672 (after Hedrick), for the purpose of supplying new tissue to connect the parts. Here the edges of the girdle are trimmed to the fresh firm tissue, cions whittled wedge- shape at each end are inserted, bandages are drawn around the trunk to hold the free edges of the bark and the ends of the cions, and wax is poured over the work. This operation is performed in spring, with dormant cions. The buds should not be allowed to throw out shoots. If the cions are placed close together, they will soon unite along their sides and make a continuous covering of the wound. Writing of bridge-grafting, Hedrick says (N. Y. Sta. Circ. No. 17): "Its most important use is to preserve trees injured or girdled by rodents or disease. Any ragged or diseased edges should be cleanly cut away, a longitudinal slit should be made in the bark, both above and below the wound, and the edges of the slits loosened slightly. A cion should then be cut 2 or 3 inches longer than the space to be bridged, one side beveled off at both ends (Fig. 1672), and inserted in the slits, its beveled face against the wood
of the trunk. In order to guard against any accidental displacement it would be well to drive a small tack or nail through each end of the cion, which, however, must not be split in the operation. Other cions in a like manner may be inserted at intervals of about 2 inches over the entire injured surface. The ends of the cions should be covered with wax but it is not necessary to cover all the bridged portion of the trunk. If the tree operated upon is small and likely to weave in the wind it should be tied firmly to a strong stake as such movements might tear apart the tender uniting surfaces."
Cions are sometimes inserted freely in the stub left by a large broken limb, for the double purpose of providing other shoots to take the place of the branch and of facilitating the healing of the wound. Sometimes cions are inserted in limbs on a one-sided or misshapen tree for the purpose of securing better growth on that side, the variety perhaps being the same as that of the tree itself.
Another reason for grafting is to produce some radical change in the nature of the cion, as rendering it more dwarf, more fruitful, or otherwise changing its habit. Still another office is to adapt plants to adverse soils or climates. An example is the use of the peach root in the southern states upon which to work the plum, as the peach thrives better than the plum in sandy soils. The practice in Russia of working the apple on roots of the Siberian crab is an example of an effort to make a plant better able to withstand a very severe climate.
In general, however, grafting is employed for the purpose of multiplying or perpetuating a given variety, mostly of woody plants. It is used with plants that do not bear seeds, or in which the seeds do not come true or are difficult to germinate, or when the plants do not propagate well by cuttings or layers. It is also employed to increase the ease and speed of multiplying plants.
In common practice, the effect of the stock on the cion is rather more mechanical or physical than physiological or chemical. The influences are very largely those associated with greater or less growth. As a rule, each part of the combined plant—the stock and cion— maintains its individuality. There are certain cases, however, in which the cion seems to partake of the nature of the stock; and others in which the stock partakes of the nature of the cion. There are recorded instances of a distinct change in the flavor of fruit when the cion is put upon stock that bears fruit of very different character. There are some varieties of apples and pears which, when worked on a seedling root, tend to change the habit of growth of that root. Examples are Northern Spy and Whitney apples, which, when grafted on a root of unknown parentage, tend to make that root grow very deep in the soil. All these instances seem to be special cases, or exceptions to the general rule that each part maintains its individuality. Reasons for this change of nature in these cases have not been determined, and in most cases such results are not to be predicted. The most marked effect of stock on the cion is a dwarfing influence. Dwarfing may be expected whenever the stock is of a smaller stature than the cion. The most familiar example is the dwarf pear, made by working the pear on quince stock. Supplying a plant with a slow-growing root is only the beginning of the making of a dwarf. The plant must be kept dwarf by subsequent pruning and other care. There is comparatively little demand for large-growing forms of woody plants, whereas there is much demand for dwarf forms. See Dwarfing, page 1082.
The limits within which grafting can succeed are to be determined only by experiment. These limits are often within the species, and usually within the genus, but there are instances in which plants of distinct genera intergraft with success, as in some of the cacti. In general, the closer the affinity of cion and stock, the better the union. When stock of the same species cannot be secured, it is allowable to chose another species. Thus it was for a time impossible to secure Japanese plum stocks upon which to grow the varieties of Japanese plums, and peach, Marianna, myrobalan and domestica plum stocks have been used, and are used to this day. In some cases another species grows more readily from seed, is cheaper, is less liable to fungous injury in the nursery, or has some other practical advantage. Thus, most domestica plums (Prunus domestica) in the North are worked on the myrobalan (P. cerasifera); many sweet and sour cherries (Primus avium and P. Cerasus) are worked on the mahaleb (P. Mahaleb); many kinds of roses are worked on mahctti and Rosa multiflora stocks.
From time to time there arises an agitation against grafting, particularly in the Old World. Cases of poor unions and the difficulties of sprouting from the root or stock are cited as proofs that graftage is injurious and devitalizing. But these are examples of poor results. They show what should not be done. Properly performed, on plants of proper affinity, graftage is not devitalizing. It is essential to modern horticulture.
The ways or fashions of grafting are legion. There are as many ways as there are ways of whittling. The operator may fashion the union of the stock and the cion to suit himself; if only he apply cambium to cambium, make a close joint, and properly protect the work. Thus, Thouin in his "Monographic des Greffes," 1821, ' describes 119 kinds of grafting. All kinds of grafting may be classified into three groups:
1. Bud-grafting or budding. In the old days called inoculation.
2. Cion-Rrafting, or what is now thought of as grafting proper.
3. Grafting by approach, sometimes called inarching.
Early practice.
Grafting is one of the oldest of the arts of plant-craft. It is probable that the real art of grafting was held more or less as a professional or class secret in the ancient world, for the writers seem to have only the vaguest notion of its possibilities and limitations. Virgil writes (Preston's translation):
But thou shalt lend
Grafts of rude arbute unto the walnut tree,
Shalt bid the1 unfruitful plane sound apples bear.
Chestnuts the beech, the ash blow white with the pear.
And, under the elm, the sow on acorns fare.
It seems to have been a popular misconception that any kind of plant will grow on any other. Pliny .asserts that the art of grafting was taught to man by nature. Birds swallow seeds, and these seeds, falling in "some cleft in the bark of a tree," germinate and make plants. "Hence it is that we see the cherry growing upon the willow, the plane upon the laurel, the laurel upon the cherry, and fruits of various tints and hues all springing from the same tree at once." This, of course, is not grafting at all, but the implanting of seeds in earth- filled chinks and cracks, in which the plants find a congenial foothold and soil. But the ancients have left us abundant testimony that genuine grafting was employed with success. Pliny describes a cleft-graft. He gives several precautions: the stock must be "that of a tree suitable for the purpose," and the graft must be "taken from one that is proper for grafting; the incision or cleft must not be made in a knot; the graft must be from a tree "that is a good bearer, and from a young shoot;" the graft must not be sharpened or pointed "while the wind is blowing;" "a graft should not be used that is too full of sap, no, by Hercules! no more than one that is dry and parched;" "it is a point most religiously observed, to insert the graft during the moon's increase."
[[Image:Apple tree grafting 3.jpg|thumb|400px|Numerous grafts in one spot.]]
[[Image:Apple tree grafting 3.jpg|thumb|400px|Numerous grafts in one spot.]]
[[Image:Budding (PSF).jpg|thumb|300px|Budding.]]
[[Image:Budding (PSF).jpg|thumb|300px|Budding.]]