of the Stock on the Scion, and vice versa.
Essay by Josiah Hoopes, for the American Pomologlcal Society.
BOTH theory and practice teach us that the relationship existing between the root and the top of a tree cannot be impaired to any great extent, by any artificial intervention of man. The very moment that an inserted bud or graft commences to granulate and then unite, that moment the two parts of the embryo tree struggle, as it wer, for the mastery. That is, certain idiosyncrasies inherent either in the branches of the one, or the roots of the other, will form a leading feature in the mature plant. Abundant proof of this is afforded by examining the roots of nursery-grown apple trees, whether budded or grafted. Take for instance some well-known variety, as the Bellefleur, and the roots will be found uniformly long, slender, and very fibrous; other kinds will prove exactly the opposite. If we place a graft of some well marked variety upon any ordinary stock, say five or six feet high, in a few years certain peculiarities of the bark will be found extending down from the branches to the body of the tree; as is instanced in the Newtown Pippin Apple, and Van Mons Leon le Clerc Pear. Another curious feature respecting the influence of the scion upon the stock, is noticeable in some of the so-called "sports," or variegated leaved plants.
During the past season, a Mountain Ash, upon which was budded a variety with variegated leaves, commenced to push forth young shoots from the main body of the tree, below the point where the bud was inserted. In every case these had variegated leaves. Now, in view of the fact that these adventitious buds were there in advance of the original variegated bud, the presumption is, that they were created green, and their normal condition yielding to the controlling influence of the new branches, caused the change to occur by the flow of sap from above.
A still more remarkable case than the one above cited, was related some time since by a correspondent of the London Garden. He states that he procured scions of a diseased Horse Chestnut with yellow leaves, and worked them upon strong, healthy young trees. Some time thereafter, upon examining the stocks where the scions had failed, young shoots were found down the body, bearing the identical yellow-hued foliage; and yet, where the buds originally inserted had "taken," they produced perfectly healthy green leaves.
This disease, for I hold that all variegation is in some manner unhealthy, had evidently been communicated from the bud or scion to the stock before the death of the former, and for a short time, during its vain struggle for existence, contaminated the parts below.
The Scientific Committee, of the Royal Horticultural Society of England, also records a like case with a yellow-leaved Laburnum. After the inserted bud had died, variegated shoots were noticed issuing from the stock, both below and above the inserted point. And Dr. Masters, the English botanist, has stated that an Abutilon had thrown out variegated shoots after grafting with a variegated variety, but ceased to do so after the inserted graft died.
But, in some instances, the stock exerts a marked influence upon the scion, thus showing the co-operative system in use between them. The Gardener's Chronicle mentions an instance of a couple of Muscat vines worked on the Black Hamburgh, in the same house with a Muscat, on its own roots. Those worked on the Hamburgh start fully five or six days in advance of the one on its own roots, although they are nearly a fortnight behind the Hamburghs they are worked on. It is a curious fact that there has never been seen any difference in the ripening season, nor any effect on the fruit.
As we stated in the commencement, certain marked peculiarities will, sooner or later, always make themselves known; sometimes it will be one thing, and again another and totally different feature assumes the superiority. The governing cause, involved in mystery as it is, to a certain extent, affords us a clue by means of which we may study a very useful lesson in plant life.
We know that all vegetable growth arises from a cell, and what is termed young shoots, leaves, blossoms, etc., are, in fact, but an accumulation of cells, which, in time, develop woody fibre and other organs. The propagator of new varieties knows that a single bud, or a section of a young branch, may be inserted in a different tree, and these will unite and produce fruits and flowers similar to the kind from which said bud or graft was taken. Now, let us inquire into the changes that occur during this growing process, or, as horticulturists term it, "taking." Between the wood and bark is where active growth takes place, and the layer of young cells found here is known as the Cambium layer. All growth, of whatever nature, is by cells, the origin of which is, however, at present unknown. But this cell-growth is accomplished by small protuberances, making their appearance on the walls of the older cells, and these rapidly increase, and again, in turn, assist in the formation of others, and this is carried on so long as growth takes place. Without going into a long dissertation upon the subject of cell-growth, which would form a long essay in itself, I will merely state that the question has been asked in relation to a budded tree, can the cells, at the point of union, be partly of one variety and a part belong to another? My theory is, that a cell, singly, is entirely a component part of the variety from which it originates, either from the scion or stock, and is invested with all the powers and principles inherent in that part. A single cell cannot be of two varieties, but a collection of cells, as, for instance, the cellular tissue, may be formed partly of both. The vascular or fibrous tissue is governed by the same laws, each separate, but the little bundles of woody tissue uniting by their outside covering or walls, thus forms a compact mass of wood, and the bud or graft has taken, which ultimately forms the future tree.
A bud is, in fact, an embryo tree. It contains within its protective covering all the elements of tree growth, with all the organs of vegetation and reproduction intact. Therefore, when a bud is inserted beneath the bark of another plant, the cellular growth at once takes place on both sides, these unite by their outside walls, and the so-called sap commences to circulate in the inter-cellular passages from one to the other. It is, therefore, no wonder that certain peculiarities embraced in the root may be found developing in the scion or top, and vice versa. That the scion is enabled to reproduce its kind, is due to the fact that its young growth is merely an increase of cells already formed, and the variations alluded to at the commencement of this paper are the result of constant currents of sap flowing between the two remote portions of the tree, and at the same time imbuing the one with certain marked characters, contained previously in the other.
Thus, in a somewhat hurried, and I fear very imperfect manner, I have alluded to the influence of the stock upon the scion, and vice versa.
This interesting subject is by no means all theory, as many suppose, but is the result, for the most part, of close examination by means of the powerful lens. Future investigation will, undoubtedly, reveal many novel features which we now know not of, and to accomplish this fully, the patient student of horticulture is asked to join the botanist in the pleasant task.
But there is another and more popular aspect to this subject—the relative advantages of certain stocks for particular species of plants. Under this heading, we may take for example the plum worked on the peach. Prejudice and distrust, on the part of many cultivators, have done this operation great injustice. To the owner of a heavy soil, where the plum root thrives luxuriantly, peaches should be planted with caution; but, on the other hand, in the great peach districts, with a light mellow soil, the peach root will succeed far better than the plum. Peaches always make a large number of strong fibrous roots, and return to the top a vast amount of nutrition. The junction in certain varieties of plum on peach roots is perfect, and the tree is long-lived and healthy.
The testimony of some of our most noted pomologists go to show that the practice is correct, and a careful examination plainly indicates that the theory is faultless as well.
The subject of dwarfing fruit trees is not properly understood. The pear worked on quince roots certainly dwarfs the tree to a certain extent, and for a few years, but is the process caused by some inherent property contained in the quince? We think not. Once allow the pear to throw out a few roots above the point of junction, and the tree becomes a standard. The abundance of sap or nourishment gathered up by the roots and forwarded to the top, causes in most cases a larger and finer growth of fruit, thus showing that the quince is adapted to these kinds; but take an uncongenial variety, and mark the result. The fruit is often in such eases worthless. Years ago we were told that budding cherries on the Mahaleb stock would cause the trees to become dwarf. Little did these propagators know that when they annually pruned their trees, this was what dwarfed them, and not the root. The junction in this case is always perfect, and it is a well-known scientific fact, that excessive pruning causes debility in a plant, and that, when vitality is checked, the tree becomes dwarfed, as a matter of course. Excessive growth and productiveness seem to be generally antagonistic. A dwarf tree, after the first vigorous growth is over, will, if healthy, produce good crops and mature a reasonable amount of new wood. Some certain varieties of pears, as, for instance, the Bartlett, never unite properly on the quince stock—the cellular tissue of each never seems to make a perfect union. Very many trees that we have examined under a strong lens reveal a marked line between the cell-growth of the two, and not, as is the case with other kinds, a lengthening of both cell-growths, one up, and the other down, so that it is very difficult to determine where the exact point of insertion really is. There are causes, over which we have no control, that debar us from dwarfing some varieties, but science has not yet solved the mystery. JOSIAH HOOPES.