This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
In the 5th number of the present volume of the Horticulturist is an article headed "Bad Grafting - How wood is formed," taken from the "Gardener's Chronicle." The conclusions of the writer do not appear to be consistent with correct principles of vegetable physiology, principles now being received and explained by the late discoveries of the microscope in regard to growth, and which give a satisfactory explanation of that phenomenon. The positions advanced are based upon the supposition of the downward flow of sap in forming new wood, and that this sap is vitalized by the action of light in the leaves. A plate is given in which is shewn a large stock on the side of which a small scion had been whip-grafted upon "one side," and after growing together some time, "upon applying a little lateral pressure the scion came away," as represented in the cut, "bringing with it a considerable quantity of young wood." From these representations the conclusion is arrived at, that "the scion had formed a woody sheath of its own, which covered over the wood of the stock and was independent of it," and that "it is obvious, indeed, that the new wood is really derived in either a solid or liquid form from the two branches," that is, of the graft.
That these conclusions are incorrect, I propose to show, first, that no growth ever takes place in a graft but by the ascent of sap from the stock. We who are in the habit of grafting, know that, unless the union of the inner bark of the stock and graft is so close as to admit of the passage of sap upward, no growth can take place in the graft. It does not possess the power to send down growth to cover up the stock. When freshly cut wood, such as that of the stock and graft, is excluded from light and kept in a moist condition, granules of new wood are emitted at the junction of the wood and bark, but nowhere else; and if the two are in proper position, a union takes place from the affinity of each for the other; and this takes place before even the buds of the graft begin to swell, and before any leaves are developed to aid in sending down material for new wood as contended for.
Secondly, this theory of the downward flow of matter for new wood is shewn not to be true. The discoveries by the microscope have shewn, that growth is made by the deposition of cell matter, and that these cells are formed from matter imbibed by the sap from the soil, and deposited where formed; some are added to the extremities of the spongioles or rootlets, and thus the root is elongated; others are added at the sides to increase in size; and thus all the way upward they are deposited to form new layers of wood, and to fill up the pores of the sap-wood and gradually form heart-wood. The author of the article on botany, in the new American Encyclopaedia now published, shows conclusively, that, considering the vast amount of water known to be given off by the leaves, and that this amount being taken in by the roots and containing mineral matter, or wood-forming matter, even in small quantities, there is abundant reason to conclude that sufficient is imbibed to account for all the growth we see.
The downward flow of sap is by this writer entirely rejected.
In a late number of the American Farmer, is an article translated from the Flore des Serres, published in Belgium, by one of the editors, in which is the following paragraph: "Modern chemistry has afforded us many lights upon the nature of the elements that constitute the nourishment of plants, and if certain doubts or errors upon this subject still exist, they must not be attributed to science - that is always true - but to prejudices, of which unhappily we are not always willing to divest ourselves. Thus it is not correct to believe that the sap is elaborated and modified in the leaves, and that it redescends thence in the bark down to the roots. In fact, that is not possible. Doubtless the carbonic acid is decomposed in the leaves, but that act has no direct connection with the nutrition of the plant; it has as its sole object the preservation of the leaves for the purpose of transpiration. This truth will one day be generally recognized, when physiology shall have furnished the proof that the functions of leaves can only consist in transpiration, and that, in order to be able to fulfil these functions during their continuance, it is requisite that the cells of the parenchyma should be continually renewed".
Electricity is acknowledged to play an important part in the phenomena of growth, and the well known fact of the increase of growth by electrical action, together with the further known fact of the power of electricity to release oxygen from its compounds, and thus decompose carbonic acid gas, is strongly confirmatory of this view. The air and the earth are often posi-. tire and negative to each other; sometimes it is extremely difficult to excite electrical action by a machine, at other times it is easily done.
When the air is positive and the earth negative, every point of a leaf and every twig is a conductor to receive and convey the electricity to the earth; and as it has a strong affinity for water, it passes through the sap exactly in the place to meet the carbonic acid gas, and decompose it precisely when needed for growth. Carbon being positive is deposited, while the oxygen being negative is given off, exactly as is done in the process of electro-typing. The same effect is produced when the earth is positive and the air is negative.
This principle being admitted, we have a satisfactory explanation of the "puzzling phenomena" that we meet with, and which have puzzled and ever will puzzle those who rely on a downward flow of sap. Water taken in by the spongioles and rootlets containing carbonic acid, and other matters derived from the soil, and carried up as sap, and in its passage being decomposed and deposited as growth in the plant, will account for all we see in growth. Fruit grown from a graft will be of the variety of the graft, and from the stock will be its variety; thus we get clear of the difficulty met with by those who contend for the downward formation of wood, and find the stock to produce not the variety of the graft but its own.
This writer speaks of a willow which formed a sheath of wood several feet long over dead wood and beneath dead bark 1 I myself had a willow that was cut down about four feet above the ground; and on one side shoots put out near the top and grew to considerable size, at the same time the other side of the stump died and became rotten; when afterwards in removing the rotten part it was found that roots had put out of the new growth and descended through the rotten wood to the ground. Here is nothing strange; roots ordinarily never put out in the open air, - but in a dark moist condition, when materials for growth are to be had, they always do so under favorable circumstances; and the putting forth of roots under dead bark, only shows the efforts of nature to overcome impediments to growth.
In the plate referred to, there is a cross-section of the head of the stock and the insertion of the graft, showing the deposit of new wood near this junction alone. This is just what we might have expected, as no wood could be deposited but where a flow of sap could take place; consequently, on the side opposite to the graft there could be none. The cut parts of a graft and stock never unite, it is only the addition of layers of new wood enclosing them that makes a union.
This writer considers there are "two distinct systems of organization in our common trees, the one longitudinal, a mere provision for carrying the sap, - the other horizontal, called the medullary system;" and that " the latter alone has the power of furnishing new shoots;" that " it is perpetually growing outwards and fitting on its myriads of extremities to the surface of the wood beneath the bark;" and these two are simultaneous in their appearance, and coexistent and coeval, but independent." To this it may be objected, that as the "medullary system," however important a part it may act, cannot be increased or continued in growth, but by the " provision for conveying the sap," it cannot be "independent" as claimed by this writer. "New shoots " are formed only by the accumulation of sap, and to say that "the provision for its conveyance" has no "power of furnishing new shoots," is giving "the medullary system" a character that known facts will not warrant It has no power of increase, no separate action of its own, but is dependent entirely on the circulation of the sap for any increase.
To suppose that new shoots "necessarily come from the horizontal or medullary system," is making a distinction without a difference, for we all know that "the system for the conveyance of the sap" is included in every shoot, and without it it could not live nor exist. Many kinds of deciduous trees, if cut down in winter, on the approach of spring, by the accumulation of sap, will put out new shoots around the stump and grow off rapidly. Whether they are based on "the medullary system" or not, they are produced by the accumulation of sap, and that often where no previous buds had existed. Some writers have appeared to believe that they only appear where latent buds have existed; but this view is not borne out by facts. Their number is often many times more than the number of buds that ever existed in the same length, and even if there had been latent buds, where were they? they only could be in the outer epidermis or dead part of the bark, and could in no case have any connection with the living tissue, from which alone the shoots took their rise.
What the writer means by the terms, "physiological heretics" and "orthodox" in this question, is not easy to see; the science of vegetable physiology is too young yet for any but the credulous to assume the title of orthodox in its profession, and brand others as heretics. It may be with this as it has been with religion: those who by the majority were called heretics, were in truth the really orthodox, while those who claimed that title, by their actions gave the lie to their professions.
The animadversions of this writer on improper trimming of fruit trees are well-timed, and should be heeded by all who wish to take nature for their guide, and conform their action to her laws; but there is another kind of mutilation that is doing incalculable injury to the orchards in this country, and that is the deep cultivation in cropping our orchards. We cut and tear off all the surface roots of our trees, and compel them to force their roots down into a colder and more barren soil, barren at least of vegetable matter, and if we apply manure the crop is benefited but not the trees. This manner of treatment has injured our orchards greatly, and we shall ultimately find that we shall have to treat our orchards as we do our other crops, - allow them to have the full benefit of the surface soil, and grow no other crop with them, at least after the trees attain some size. If fruit is an object it is worth while to appropriate land to it alone; if it is not an object, trees should not be permitted to occupy the land to the detriment of other crops.