Transactions of the Horticultural Society of London 2:199-204 (1822)
XLIX. On the Effects of different Kinds of Stocks in grafting.
Thomas Andrew Knight, Esq. F. R. S. &c. President.
Read February 6, 1816.

*See page 19 of this volume.

THE practice of propagating fruits of different species, by grafting upon stocks of other species, has been so extensive, both in ancient and modern times, that the good and ill effects of it can scarcely be supposed to have escaped the observation of gardeners. Accurate information upon this subject can, however, only be acquired by experiments accurately made, and closely attended to, during many successive years, upon the comparative good and ill effects of stocks of different species, when growing in soils of the same, and of different qualities: and no such experiments, have, I believe, ever been made in this country, nor, to a proper extent, in any other. DU HAMEL has pointed out, with his usual ability, the erroneous opinions entertained by his countrymen upon this subject, and has given some valuable information, which I have cited in a former communication;* but he admits, that relatively to some very important points, he only details the opinions of others; and he laments that he has not himself made the experiments necessary to decide the questions, which he wishes to investigate. I also feel, that I am not, by any means, master of the subject upon which I have taken up my pen to write: but I believe, that I have made and seen the result of more experiments, during the last thirty-five years, than any other person; and I venture to hope, that my experience enables me to draw a few conclusions, which may prove useful.

*Vol. i. page 108. **The Abricot-Peche, or Abricot de Nancy of the French.

Whenever the stock, and graft, or bud, are not perfectly well suited to each other, an enlargement is well known always to take place at the point of their junction, and generally to some extent, both above and below it. This is particularly observable in Peach trees, which have been grafted, at any considerable height from the ground, upon Plum stocks; and it appears to arise from obstruction, which the descending sap of the Peach tree meets with in the bark of the Plum stock; for the effects produced, both upon the growth and produce of the tree, are similar to those which occur when the descent of the sap is impeded by a ligature, or by the destruction of a circle of bark, in the manner recommended by Mr. Williams in a former volume of the Horticultural Transactions.* The disposition in young trees to produce and nourish blossom buds and fruit, is increased by this apparent obstruction of the descending sap; and the fruit of such young trees ripens, I think, somewhat earlier than upon other young trees of the same age, which grow upon stocks of their own species; but the growth and vigour of the tree, and its power to nourish a succession of heavy crops, are diminished, apparently, by the stagnation, in the branches and stock, of a portion of that sap, which, in a tree growing upon its own stem, or upon a stock of its own species, would descend to nourish and promote the extension of the roots. The practice, therefore, of grafting the Pear tree on the Quince stock, and the Peach and Apricot on the Plum, where extensive growth and durability are wanted, is wrong; but it is eligible wherever it is wished to diminish the vigour and growth of the tree, and where its durability is not thought important. The last remark applies chiefly to the Moor-park Apricot.**

When great difficulty is found in making a tree, whether fructiferous, or ornamental, of any species, or variety, produce blossoms, or in making its blossoms set when produced, success will probably be obtained in almost all cases, by budding or grafting upon a stock which is nearly enough allied to the graft to preserve it alive for a few years, but not permanently. The Pear tree affords a stock of this kind to the Apple; and I have obtained a heavy crop of Apples from a graft which had been inserted in a tall Pear stock, only twenty months previously, in a season when every blossom of the same variety of fruit in the orchard was destroyed by frost. The fruit thus obtained was externally perfect, and possessed all its ordinary qualities; but the cores were black and without a single seed; and every blossom had certainly fallen abortively, if it had been growing upon its native stock. The experienced gardener will readily anticipate the fate of the graft: it perished in the following winter. The stock, in such cases as the preceding, promotes, in proportion to its length, the early bearing and early death of the graft.

*Vol. i. page 216.

The authority of Duhamel gives us reason to believe, that the defects of particular soils may be remedied by a proper selection of stocks; and that cases may occur, in which it will be eligible to bud the Peach and Nectarine upon the Apricot or Plum. My own experience induces me to think very highly of the excellence of the Apricot stock, for the Peach or Nectarine; but wherever that, or the Plum stock is employed, I am confident the bud cannot be inserted too near the ground, when vigorous and durable trees are wanted. The opinion of Mr. Wilmot, in a former Volume of our Transactions* is, upon this point, opposed to mine; but I speak upon the evidence of long experience, and of experiments accurately and purposely made with my own hands.

The form and habit which a Peach tree of any given variety is disposed to assume, I find to be very much influenced by the kind of stock upon which it has been budded: if upon a Plum or Apricot stock, its stem will encrease in size considerably, as its base approaches the stock, and it will be much disposed to emit many lateral shoots, as always occurs in trees whose stems taper considerably upwards; and, consequently, such a tree will be more disposed to spread itself horizontally, than to ascend to the top of the wall, even when a single stem is suffered to stand perpendicularly upwards. When, on the contrary, a Peach is budded upon the stock of a cultivated variety of its own species, the stock and the budded stem remain very nearly of the same size at, as well as above and below, the point of their junction. No obstacle is presented to the ascent, or descent, of the sap, which appears to ascend more abundantly to the summit of the tree. It also appears to flow more freely into the slender branches, which have been the bearing wood of preceding years: and these consequently extend themselves very widely, comparatively with the bulk of the stock and large branches.

When a stock of the same species with the graft or bud, but of a variety far less changed by cultivation, is employed, its effects are very nearly allied to those produced by a stock of another species, or genus: the graft, generally, overgrows its stock; but the form and durability of the tree are generally less affected, than by a stock of a different species or genus.

Many gardeners entertain an opinion, that the stock communicates a portion of its own power to bear cold, without injury to the species, or variety, of fruit, which is grafted upon it: but I have ample reason to believe, that this opinion is wholly erroneous: and this kind of hardiness in the root alone can never be a quality of any value in a stock; for the branches of every species of tree are much more easily destroyed by frost, than its roots. Many also believe, that a Peach tree, when grafted upon its native stock, very soon perishes; but my experience does not further support this conclusion, than that it proves seedling Peach trees, when growing in a very rich soil, to be greatly injured, and often killed, by the excessive use of the pruning knife upon their branches, when those are confined to too narrow limits. The stock, in this instance, can, I conceive, only act injuriously by supplying more nutriment than can be expended; for the root which nature gives to each seedling plant must be well, if not best, calculated to support it; and the chief general conclusions which my experience has enabled me safely to draw, are, that a stock of a species, or genus, different from that of the fruit to be grafted upon it, can rarely be used with advantage, unless where the object of the planter is to restrain and to debilitate: and that where stocks of the same species with the bud, or graft, are used, it will generally be found advantageous to select such as approximate in their habits, and state of change, or improvement, from cultivation, those of the variety of fruit which they are intended to support.