CHAPTER IV.
MODES OF PROPAGATION BY DIVISION, viz. TAKING OFF SUCKERS, MAKING LAYERS AND CUTTINGS, BUDDING, GRAFTING, AND INARCHING.
Properly speaking, there are only two modes of propagating plants, viz.: by seed and by division. The first raises a new individual, resembling the plant that produced the seed, as a child does its parent, but not perpetuating any accidental peculiarity; and the second method multiplies specimens of the individual itself. Species are propagated by seed, and new varieties are raised; but varieties are generally propagated by division, as they do not always come true from seed. Propagation, by division, may be divided into two kinds:—those in which the young plants root in the ground, such as suckers, layers, and cuttings; and those in which they are made to root in another plant, as in budding, grafting, and inarching.
Suckers.—Sending up suckers, forming offsets, and throwing out runners, are all natural ways of propagation that require very little aid from the hand of man; and if all plants produced these, nothing more would be required than to divide the offspring from the parent, and replant it in any suitable soil. But only certain plants throw up suckers, such as the rose, the raspberry, the lilac, the English elm, &c. Offsets are only formed on bulbs, and runners are only thrown out by strawberries, brambles, and a few other plants; and thus these modes of propagation are extremely limited in practice. No plants produce suckers but those that send out strong horizontal roots; and the sucker is in fact a bud from one of these roots which has pushed its way up through the soil, and become a stem. As this stem generally forms fibrous roots of its own, above its point of junction with the parent root, it may in most cases, when it is thought necessary to remove it, be slipped off the parent and planted like a rooted cutting. As, however, the nourishment it can expect to derive from its own resources will be at first much less than what it obtained from its parent, it is customary, when a sucker is removed, to cut in its head, to prevent the evaporation from its leaves being greater than its roots can supply food for. Sometimes when the parent is strong, part of the horizontal root to which the sucker was attached is cut off and planted with the young plant.
Suckers of another kind spring up from the collar of the old plant, and when removed are always slipped, or cut off, with the fibrous roots that they may have made, attached. Offsets are young bulbs which form by the side of the old one, and merely require breaking off, and planting in rich light soil. Runners are shoots springing from the crown or collar of the plant, which throw out roots at their joints; and which only require dividing from the parent plant and replanting in good soil to make new plants.
Layers.—Many plants, when kept in a moist atmosphere, having a tendency to throw out roots from their joints, the idea of making layers must have very early occurred to gardeners. Where the roots are thrown out naturally, wherever a joint of the shoot touches the moist earth, (as is the case with some of the kinds of verbena, which only require pegging down to make them form new plants,) layers differ very little from runners; but layers, properly so called, are when the art of the gardener has been employed to make plants throw out roots when they would not have done so naturally. The most common method of doing this is to cut half through, and slit upwards, a shoot from a growing plant, putting a bit of twig or potsherd between the separated parts; and then to peg down the shoot, so as to bury the joint nearest to the wound in the earth; when the returning sap, being arrested in its progress to the main root, will accumulate at the joint, to which it will afford such abundance of nourishment, as to induce it to throw out a mass of fibrous roots, and to send up a leading shoot.
A Verbena layered.
The only art required in layering is to contrive the most effectual means of interrupting the returning sap, so as to produce as great an accumulation of it as possible, at the joint from which the roots are to be produced. For this purpose, sometimes, instead of cutting the branch half through, a ring of bark is taken off, care being taken that the knife does not penetrate into the wood; and at others a wire is twisted firmly round the shoot, so as to pinch in the bark; or a knife or any sharp instrument is passed through the branch several times in different directions: in short, any thing that wounds, or injures the shoot, so as to throw an impediment in the way of the returning sap, and yet not to prevent the passage of the sap that is ascending, will suffice.
Layering is a very common mode of propagating plants: and in nurseries often every shoot of a tree or shrub is thus wounded and pegged down. In this case, the central root is called a stool, from the verb, to stole, which signifies the power most deciduous trees possess, of sending up new stems from their roots when cut down. The seasons for performing the operation of layering are during the months of February and March, before the new sap begins to rise, or in June or July after all the summer supply of ascending sap has risen; as at these seasons there is no danger of injuring the tree by occasioning an overflow of the ascending sap, which sometimes takes place when the tree is wounded while the sap is in active motion. In most cases the layers are left on twelve months, and in many two years, before they are divided from the parent plant, in order that they may be sufficiently supplied with roots. In nurseries, the ground is generally prepared round each stool by digging, and sometimes by manuring; and the gardener piques himself on laying down the branches neatly, so as to form a radiated circle round the stool, with the ends rising all round about the same height.