Page images

and also of ascending in the form of stem. The first of these buds is the embryo ; the others are subsequently formed on the stem emitted by the embryo. As these secondary buds develope, their descending roots combine and form the wood, their ascending stems give rise again to new buds. These buds are all exactly like each other : they have the same constitution, the same organic structure, and the individuals they are capable of producing are, consequently, all identically the same; allowance, of course, being made for such accidental injuries or alterations as they may sustain during their subsequent growth. It is upon the existence of such a remarkable physiological peculiarity in plants, that propagation entirely depends; an evident proof of which may be seen in this circumstance.

Take a cutting of a vine consisting only of the space which lies between two buds, or an internodium, as botanists would call such a piece, and no art will succeed in ever making it become a new plant, no matter how considerable the size of the internodium may be.* But, on the other hand, take the bud of a vine without any portion of the stem adhering to it, and it will throw out stem and root, and become a new plant immediately. If we examine the various modes employed in horticulture for propagating plants, we shall find that, however different they may be in appearance, they all consist in the application of these principles under various forms. It will be most convenient to consider these methods separately.

Propagation is effected by the arts of Increasing by Eyes, Striking from Cuttings, Laying, Budding, and Grafting.

Increasing by Eyes is the simplest of all these methods : it consists in nothing but extracting a single

* This is, of course, said without reference to the power which some plants possess of developing latent buds, - a subject which is foreign to the present enquiry.

system of life, or a bud, from a given plant, placing it in due heat and moisture, and surrounding it with fitting food, and thus causing it to grow as a solitary individual, instead of as one of the community to which it originally belonged.

Striking from Cuttings is a slight modification of the last method. Instead of taking a single bud, a stem containing two, three, or more buds, is placed in circumstances fitted for the maintenance of its life. In this case, the chances of success are increased by the additional number of buds which are the subject of experiment. That bud which is the nearest the bottom of the cutting emits its roots at once into the earth, and so establishes a communication between the general system of the cutting and the medium from which its food is to be derived. The other buds, by pushing their stems upwards into light, attract the nutriment absorbed

the roots, and so stimulate the latter to increased action. Ultimately, the roots of all the buds descend between the bark and the wood until they reach the earth, into which they finally pass, like those of the first bud. There is another circumstance which renders the operation of striking plants from cuttings less precarious than from eyes.

In both cases, the buds have, at the outset, to feed upon matter in their vicinity, until they shall have formed roots which are capable of absorbing food from the earth ; but in eyes, the nutritive matter can exist only in such portions of the stem as may have been cut away with themselves; while, on the other hand, in cuttings, the stem itself forms an important reservoir of nutriment. This is a consideration, the practical importance of which will be obvious to every cultivator. As it is from the buds alone of cuttings that roots proceed, it follows, that in cases of difficulty, when plants strike unwillingly, any thing which may facilitate the immediate introduction of roots

into the soil will be advantageous. It is for this reason that a good operator always takes care, that the lower end of his cutting is pared down as close to the base of a bud as may be practicable without actually destroying any part of the bud itself; by this means the first emitted roots, instead of having to find their way downwards between the bark and wood, strike at once into the earth, and become a natural channel by which nutriment is conveyed into the general system of the cutting.

Laying is nothing but striking from cuttings that are still allowed to maintain their connection with the mother plant by means of a portion at least of their stem. Where roots are emitted with great readiness, simply bending a branch into the soil, leaving its point above ground, is sufficient to ensure the success of the operation ; but in cases of difficulty other expedients are resorted to, all which will still be found to have reference to the emission of roots by buds. One common practice is, to head down the branch that is laid into the earth; this is to call into action the buds below the incision, by stopping the general axis of development. Another method is to tongue the layer, that is, to split the stem just up to the origin of a bud; a practice that has the effect of enabling the roots to be emitted into the soil through the wound more readily than if they had to pierce through the bark; the resistance offered to their passage through the bark is in many cases so great as to compel them to continue to make wood rather than to appear in the form that is necessary for the success of the cultivator.

Budding and Grafting are operations that equally depend for their success upon the property that buds possess of shooting roots downwards and stems upwards; but in these practices the roots strike between the bark and wood of the stock, instead of into the earth, and form

new layers of wood instead of subterranean fibres. The success of such practices, however, depends upon other causes than those which influence the growth of cuttings. It is necessary that an adhesion should take place between the scion and the stock, so that when the descending fibres of the buds shall have fixed themselves upon the wood of the stock, they may not be liable to subsequent separation. No one can have studied the economy of the vegetable kingdom without having remarked that there is a strong tendency to cohesion in bodies or parts that are placed in contact with each other. Two stems are tied together for some purpose : when the ligature is removed, they are found to have grown into one : two Cucumbers accidentally placed side by side, or two Apples growing in contact with each other, form double Cucumbers or double Apples; and most of the normal modifications of the leaves, floral envelopes, or fertilising organs, are due to various degrees of cohesion in contiguous parts. This cohesion will be always found to take place in the cellular tissue only, and never in the vascular tissue. In the stems of all such trees as are grafted by orchardists, the cellular tissue is found alive only in the medullary rays and the liber; it is therefore essential, in the first place, that those parts, both in the stock and the scion, should be placed in contact. In regard to the medullary rays, these are so numerous and so closely placed that it is scarcely possible that a portion of one stem should be applied to another without the medullary rays of both touching each other at many points. No care, therefore, is required to ensure this, which may be safely left to chance. But in regard to the liber, as this is confined to a narrow strip in both stock and scion, great care must be taken that they are both placed as exactly in contact with each other as possible, so that the line of separation of the wood and bark should, in both stock and scion, be accurately

adjusted. The success of grafting depends very much upon attention to this.

But there are other reasons why this accuracy in adjusting the line between the bark and wood of the stock and scion is so important. It is at that part that the roots of the latter pass downwards over the former; and it is also there that the substance called cambium, which serves as food for the young descending fibres, is secreted. It is obvious, that the more accurate the adjustment of the line separating the wood from the bark, the more ready will be the transmission of young fibres from the one to the other ; and that the less the accuracy that may be observed in this respect, the greater the difficulty of such transmission will be. Provided the stock and scion be of exactly the same size, the adjustment can scarcely fail to be accurate in the most unskilful hands; it is in the more common case of the scion being much smaller than the stock, that this is to be most particularly attended to.

Budding differs from grafting in this, that a portion of a stem is not made to strike root on another stem, but that, on the contrary, a bud deprived of all trace of the woody part of a stem is introduced beneath the bark of the stock, and there induced to strike root. In this operation no care is requisite in securing the exact contact of similar parts, and a free channel for the transmission of the roots of the bud between the bark and wood of the stock; for, from the very nature of the operation of budding, this must of necessity be ensured. The bark of the bud readily coheres with the wood of the stock, and secures the bud itself against all accident or injury. But if precautions of the same nature as in grafting are not requisite in budding, others are of no less moment. It is indispensable that the bud which is employed should be fully formed, or what gardeners call ripe ; if it is imperfectly formed, or unripe, it may not be capable of that subsequent elongation upwards and

« PreviousContinue »