Northwest Fruit Growers' Association. 79-86 (1899)
GRAFT HYBRIDIZATION
MR. W. J. L. Hamilton, South Salt Spring, B. C.

I would like to say a word or two before I read my paper. It is on a subject which I don't think has been given the importance it should, although I don’t mean to say that I know much about it. Still, I am anxious to bring this matter forward as I wish to have any instances of Graft Hybridization on the same lines as I give in this paper related. But I would ask you to remember the one fact in support of the matter of Graft Hybridization will offset any amount of negative evidence.

The expression "Graft Hybridization," first coined by Darwin, vividly recalls to my mind the late Professor T. H. Huxley, who was his pupil, and of whose pupils I, in turn, was one.

These two great biologists, both of world-wide renown, were to the best of my belief the first to investigate this subject in a scientific manner. Data, however, were scarce, and without these even the leading biologists of their day found themselves in a very disadvantageous position, which precluded them from establishing the laws governing the interchange of properties between stock and cion. Nor is this to be wondered at when we consider the vast series of complex problems involved and the consequent and only too frequently insuperable difficulties met with in ascertaining the laws ruling the conditions of any creature organized by vitality. Few, if any, orchardists have gone sufficiently deeply into biological studies to recognize how far reaching are the laws governing the workings of nature, and so they have been too much wont to beg the question by saying that the mutual effects of stock and cion are mechanical rather than physiological.

To any student of biology this view appears to be, to say the least of it, questionable, although the difficulties involved in establishing the effects of stock on cion, and the converse, render a direct contradiction to this assertion very hard to prove. In the first place the pressure of business, and, too frequently, the lack of observation on the part of nurserymen, also the early age at which his stock is sold, generally before fruit has been produced, lose us many data which would prove, most valuable.

Again, the fact that the roots on which the cions (whether buds or grafts) are inserted, are from seeds of unknown parentage, and consequently of unknown hereditary tendencies, militates against accurate evidence, even where, as is frequently the case, some difference, however slight, is observed between the cion and the parent from which it is taken. For some of the instances of graft hybridization which I propose to quote, I am indebted to the Encyclopedia Britannica, some of Prof. L. H. Bailey's works, and also the Cyclopedia of American Horticulture, all authorities of undoubted reliability.

Others, again, have been the results of my own observation, and all of these, whether my own, or observed by others, tend to prove that graft hybridization is far from being the rare phenomenon it is generally believed to be. I am, in fact, disposed to regard it as the invariable result of grafting, though, in most instances, the changes effected are so slight as not to be readily noticeable. In this I am at variance with the Cyclopedia of American Horticulture, from which I quote the following paragraphs.

"As a rule, each part of the combined plant — the stock and the cion — maintains its individuality" "There are certain cases, however, in which the cion seems to partake of the nature of the stock; and others in which the stock partakes of the nature of the cion. There are recorded instances of a distinct change in the flavor of fruit, when the cion is put upon stock which bears fruit of very different character. There are some varieties of apples and pears which, when worked on a seedling root, will tend to change the habit of growth of that root."

"Examples are Northern Spy and Whitney apples, which, when grafted on a sort of unknown parentage, tend to make that root grow very deep in the soil."

*Lucien Daniel bibliography

"The researches of Daniel* show that the stock may have a specific influence on the cion, and that the resulting character may be hereditary in seedlings."

"Generic and graftage limits are not comparable. Generic are only arbitrary divisions for purposes of classification, and intergrafting, like intercrossing, has no necessary relation to these conceptions."

We all recognize the advantages of grafting apples on Paradise stock, and pears on quinces, for dwarfing purposes, and in this case the effect is, presumably to a great extent, mechanical, and due to the less vigor of the root, and also largely to the method of pruning employed. Yet it is recorded that pears on the quince are frequently larger and sweeter than they are on the parent trees, and it is also a matter of very common knowledge that apples grafted on the crab contain a larger percentage of malic acid than if grafted on apple stocks, and that they also frequently have a greatly enhanced color.

Prof. Bailey, in his valuable "Nursery Book" says, "Graftage may be made the means of adapting plants to adverse soils. Illustrations are numerous. Many varieties of plums, when worked on the peach, thrive in light soils, where plums on their own roots are uncertain. Conversely some peaches can be adapted to heavy soils by working on the plum."

"If dwarf pears are desired on light soils, where the quince does not thrive, recourse is had to grafting on the Mountain Ash, or some of its allies." "In some chalky districts of England the peach is worked on the Almond. Some plums can be grown on uncongenial loose soils by working them on the beach plum. Prof. Budd states in 'Garden and Forest' for February 12, 1890, that the Gros Pomier apple is particularly adapted to sandy land and the Tetofsky to low prairie land, and that these stocks are often selected to overcome adversities of soil. Such instances are frequent, and should demand greater attention from cultivators."

This last sentence is most true, and is, of itself, a sufficient reason for my giving such a lengthy quotation. Also, in the broader sense, all the above are graft hybrids, and the object of my paper is to show the actual commercial advantages to which a closer investigation of the phenomenon of graft hybridization might lead.

This is further shown by another quotation from Prof. Bailey. "Graftage often modifies the season of ripening of fruit. This is brought about by different habits of maturity of growth in the stock and cion. An experiment with Winter Nellis pear showed that fruit kept longer when grown upon Bloodgood stocks than when grown upon Flemish Beauty stocks. The latter stocks, in this case, evidently completed their growth sooner than the others. Twenty Ounce apple has been known to ripen in advance of its season by being worked upon Early Harvest."

"Mr. Augur cites an instance in which the Roxbury Russet, grafted upon the Golden Sweet, which is early in ripening, was modified both in flavor and keeping qualities. Keeping qualities is but another expression for 'season of ripening.' These influences are frequent; in fact they are probably much commoner than we are aware."

Quite so, though in my opinion these influences must, from the nature of the union of stock and cion, be not only frequent but universal where graftage is practiced.

This should be so, since the sap circulates equally through both, but, of course, is only noticed by the ordinary observer when the resultant effects are sufficiently marked to attract attention. Formerly much discussion was raised as to whether grafting is a pernicious process. The chief argument in favor of this idea being that a large amount of evidence has been forthcoming, tending to prove that graftage has produced deterioration of quality, and also has had a devitalizing effect in many cases. To my mind this goes to prove how common a phenomenon graft hybridization must be, for these instances appear to be due to injudicious unions of cions and stocks, "incompatibles," to use a druggist's phrase, whereby the union of two unsuitable varieties produced a different and inferior product. An additional argument in favor of the necessity for a careful study of the phenomenon of graft hybridization if we desire to avoid such untoward results. Perhaps, of all graft hybrids, the best sample is given in the Encyclopedia Britannica, in the article on horticulture, part of which I herewith quote.

"Of graft hybrids, the most remarkable example is Cytisus Adami, a tree which, year after year, produces some shoots, foliage and flowers like those of the common laburnum, others like those of the very different looking dwarf shrub, Cytisus Purpureus, and others again intermediate between these. We may hence infer that Cytisus Purpureus was grafted or budded on the common laburnum, and that the intermediate forms are the results of graft hybridization. Numerous similar facts have been recorded." *** "In the laburnum just mentioned, in the variegated jasmine, and in Abutilon Darwinii, in the copper beech, and in the horse chestnut, the influence of a variegated cion has occasionally shown itself in the production from the stock of variegated shoots." "At a meeting of the Scottish Horticultural Association (see Gardener's Chronicle, January 10, 1880, figs. 12 to 14) specimens of a small roundish pear, the Aston Town, and of the elongated kind known as Beurre Clairgeau. were exhibited. Two more dissimilar pears hardly exist. The result of the working the Beurre Clairgeau upon the Aston Town was the production of fruits precisely intermediate in size, form, color, speckling of rind, and other characteristics." "Similar, though less marked, intermediate characters were obvious in the foliage and flowers."

Pears appear to show the effects of graft hybridization in a more marked manner than most other fruits, and I have seen many instances of this. A Bartlett pear, grafted on a Winter Nellis, bears fruit, flowers and leaves, intermediate between the two; the fruit is comparatively small, resists scab, and in flavor is sweeter than the Bartlett, being something like the Nellis, and is clearly a hybrid.

Again, one of my neighbors had a tree of a variety he called the Pound Pear. It was not the same as the fruit thus known in England, but it equally well deserved the name, as the fruit was large, averaging over fourteen ounces each. It was a cooking pear, and, like most of its class, quite unfit to eat in its uncooked state, being harsh, hard and astringent. When ripe (February to May) it was of a yellowish tint, slightly mottled, and with a brownish cheek next the sun. It was of a very blunt conical shape, and a very vigorous grower, its only virtue being its long keeping quality. Desiring to have more of these, my neighbor grafted some cions from this tree on a Mountain Ash, some on a Bartlett, and some more on a Seckel. These cions all bore in due course, and with the following results: On the Mountain Ash stock the fruit was smaller, more conical, at least six weeks earlier, more acid, and had a clearer color, the cheek being red in place of brown. On the Bartlett stock, the pear retained its size, but, in shape and color, exactly resembled the Bartlett. In flavor it was not so harsh as its parent, though entirely unfit to eat uncooked. When cooked, however, it was more palatable than its parent, whilst its season of ripening was unaltered. On the Seckel, its form was rounder, the skin exactly the color of the Seckel, whilst flavor and time of ripening were practically unchanged. Each and every one of these pears, when compared with one another, and with the original parent, showed such marked differences that they would have been taken for different varieties. Pears and apples do not, as a rule, intergraft freely, but I have a Striped Astrachan apple grafted on a seedling pear (parentage unknown) which ripens quite a fortnight later than its parent, and that too, though it has a warmer exposure. There is, however, no noticeable alteration in its flavor.

Variegation has, I believe, been always regarded as an abnormal condition, and so, little attention has been paid to the many instances of infection of stocks by variegated cions. The same, however, might be said about nearly all cultivated fruits, for, when we compare these with their original ancestors, their abnormality becomes at once apparent.

We may therefore regard this infection as due to a genuine graft hybridization. I trust that I have now given a sufficient number of instances to convince my hearers that graft hybridism is a frequent— perhaps an invariable—result of the union of stock and cion, and I have also, I think, adduced sufficient evidence to show that its laws can profitably be investigated, with a view to better understanding how to apply them to obtain definite results.

It can then be made a potent factor, not only in improving and modifying our already existing varieties of commercial fruits, but also in extending the season of some of those which have proven themselves to be market favorites.

There appears to be ample evidence that, say, a mid-season apple can have its fruit brought to earlier maturity by grafting it on a stock which would, if allowed to bear, be a first early variety, and, if grafted on a very late ripening stock, its period of maturity could be so materially delayed, that it might be classed amongst the late apples.

Pears, however, would probably prove the best subjects to experiment on, since they appear to afford more instances of clearly defined hybrids than any other fruit, and decided results might be more quickly obtained, and the interaction between stock and cion be easier investigated. My own observations have led me to the conclusion that all vegetable life is possessed of qualities of two opposite natures, the one class being distinctly positive or assertive, whereby the individuality of each variety is maintained, whilst the other class is of a negative or unassertive nature, and is consequently over-ridden by its more powerful and vigorous positive rival.

This is in line with the principles of Mendel's law, which has hitherto only been applied to animal breeding, but he would be a bold man indeed who ventured to assert that the laws governing the animal and vegetable kingdoms differed in more than degree.

If this law holds, then the more positive combined qualities of stock and cion would be the dominant features of the graft hybrid, and of this I feel confident, although before definitely accepting this it would be desirable to find sufficient evidence accumulate to put the matter beyond a peradventure, which evidence can only be obtained by a long series of experiment from which every possible source of error is eliminated. Whilst awaiting this evidence, however, we can profitably take a glance at the processes by which both the cion and the stock are obtained. Whilst the stock is generally a seedling, it is evident that the cion also originated from a seed, so that each has an individuality or definite character inherited from the parent or parents. When these two plants are united by grafting these qualities of both stock and cion would be expected to manifest themselves. But it is only the cion which is permitted to grow, and consequently it is only in it that the interchange can assert itself.

Again, as grafts are generally inserted in stocks of the same species— apple on apple, pear on pear—the dominant characteristics of which arc frequently very similar, it is not often that the changes in nature are sufficiently marked to be observed.

When they do occur it is hard to trace them, as the parentage of the stock is usually unknown, and it is very possible that the nurseryman is blamed for sending out trees of inferior quality, or even not true to name, when the fault lies with the stock rather than the cion.

It is surely of as much importance to secure pure bred fruit trees as it is to obtain pedigreed horses or cattle. If dominating characteristics will, as they do, assert themselves in animals, it is surely logical to assume that they will follow exactly the same course in the vegetable kingdom, at any rate where the reproduction is sexual, since in the vegetable, as in the animal kingdom, sexual cells are in themselves imperfect, owing to the lack of something which the asexual cells possess, each of them, in fact, only containing half the chromosomes necessary to fertility, thereby rendering a combination necessary to perfect them These chromosomes arc believed to be the carriers of hereditary character, and as they are combined in the perfect fertile cell from the two imperfect ones, each carrying in itself the identity of its parent, it is evident that these parental characteristics, in so far as they do not neutralize one another, will be perpetuated in the resulting progeny. These characteristics will then naturally be in like manner perpetuated in the graft hybrids when the stock and cion are united, except also in so far as these individualities do not neutralize each other. It may well be asked, then, if this is so, why is not a peach modified in nature when it is grafted on a plum?

I would reply that probably it is more or less altered, but this alteration in the fruit would not be noticeable, presumably, because being a true hybrid (not a mongrel like apple on apple or peach on peach) it is probably not self fertile and would have to be fertilized by the pollen of another peach tree—cross fertilization in fact. Now the effect of this cross fertilization is very complicated, the chromosomes first uniting by the union of the two imperfect cells, and undergoing a series of structural changes, including a fusing together of the chromosomes, or rather of the ids of which they are composed, eventually resulting in the formation of an "oospore," from which develops the embryo by cell division. But this fertilizing also produces secondary results not directly concerned in fertilization, in the parts surrounding the embryo, whereby the fruit is built up. and whereby its nature is influenced, so that its appearance and flavor are affected as much by the chromosomes of the peach pollen with which it is cross fertilized, as by its own, thus minimizing any change in the nature of the fruit.

This is offered merely as a suggestion, and not as an established fact, though its probability is emphasized by the fact that comparatively few peach stones of these trees grafted on plum stocks are perfect, whereas, on seedlings, they are nearly all fertile. Where cions are grafted on their own species, however, this would not hold good, as they would be mongrels rather than hybrids, and so, self fertile, thereby rendering any changes in the fruit more apparent. It would appear then, that great care should be exercised in selecting the stocks for grafting, to see that they are adapted to the cions to be inserted, so as to avoid untoward results; and to effect this selection, care should be taken to secure seed from varieties of known character, from which to grow the stocks. Another method might be to increase by layering, but even in this case it would be advisable to use these layers only as stocks to graft on. owing to the well known fact that any species that is reproduced asexually over a long series of years, has a strong tendency to degenerate, owing to the want of infusion of fresh blood, which graftage, of course, supplies.

I trust that in this paper I have expressed with sufficient clearness that I am merely suggesting the application of Mendel's law to graft hybridism as a working hypothesis, and am by no means prepared to assert that this is really the law governing these phenomena. I believe. however, that the evidence is in favor of its applicability, and a working hypothesis is certainly needed as a centre around which to build up facts, whether pro or con, if we are to systematize these investigations

If then I can call attention to this most fascinating field for experimental research, not yet half explored, which foreshadows great possibilities of. practical results of a profitable nature, and if any interest in these possibilities is aroused, or even if any fresh facts are elicited, tending to throw more light on this interesting branch of horticultural work, I shall consider myself more than repaid for my effort to collate these facts and lay them before you.

PROF. THORNBUR—Relative to graft hybrids I would like to relate a little experience that I had at one time, while a student in college, upon the phase of graft hybrids of potatoes. We selected a dark red skinned potato and white skinned potato, cut them into pieces, being careful to split an eye in each colored potato. We tied these pieces together, matching the eyes in each instance, and planted them in pots in the greenhouse. From about one hundred grafts made in this case we secured five or six hybrids which as you will notice is a large percentage. When these plants started to grow the stems were one-half red and one-half white combining in a general way the characters of each potato. This was one of the most interesting experiments that I ever had to deal with. We also carried this one step further and selected a Russian apple known as the Pyrus Niedzwetzkyana, which has purple wood, bark, foliage, flowers and fruit and a common American apple with, of course, the white wood, green bark and ordinary flowers and fruit. We split the cions of each of these apples, being careful upon each cion to cut one or more buds in two and to tie these cions together, binding them with grafting string, we carefully callused regular callusing pits. After they were ready to plant we set them in pots in a greenhouse and from one hundred plants secured one or more graft hybrids. These particular plants showed both characters of the fruits used and while I cannot give you the final results of this experiment yet I am satisfied that we combined the qualities of the two apples by one little operation of grafting. This work is being continued at the present time in the Washington Experiment Station and we hope in the near future to secure a hardy variety by graft hybridizing.

MR. MASON—A few years ago, I planted 20 acres of orchard and I aimed to set out eight varieties. The nurseryman sold me about as many more varieties and so I sent all over the United States to get all I could and I got about 44 varieties and with what I had I had about 46 varieties and to make a long story short, I have grafted Newtons and Spitzenbergs, and I want to know whether I am going to have 60 varieties.

MR. SHARPE—I took cions of the Talman Sweet and grafted on to the Red Astrachan, produced a fruit of high color, and I waited until the cion had borne fruit, and took others from that and put on another Red Astrachan, and by the third year I was well satisfied that I had produced quite a modification. The flesh of the two varieties is quite distinct.

MR. ANDERSON—I had an experience in grafting Bartlett pears on Wild Thorn. I thought as the grafts grew well and produced very largely to all intents and purposes, the results would be good, but to the contrary they were very disappointing; the fruit did not represent a Bartlett in any shape or form and turned out absolutely worthless.

CHAIRMAN—Now, our nurserymen propagate shrubs at Shanandoah and other places and raise seedlings until they are one year old and then they are budded to any variety they wish to grow. I think our fruits are changed more by environment. I see fruits in British Columbia that are entirely different to the same varieties as those grown in our country. I think it is climatic influence. For instance where I live the Jonathan is an early fall apple. 1500 feet above that, the Jonathan is a winter apple and as I say the climatic condition makes all the difference. If the stock does not have that influence upon the cion, why have we the same Newton Pippins as in Downing's time? I would like an explanation of that.

MR. HAMILTON—I think 1 have already called attention to that, at the same time I think I have to a certain extent provided for that objection of yours. From MR. Sharpe we hear that the third generation produced marked results. As to what MR. Mason says, well I can't tell you; I hope he will be able to report as to what he does get. I have given him a jolly good excuse if he supplies the wrong varieties.

MR. MASON—I will state that the experimental station is going to keep tab on my orchard, and I have just taken a contract for 150 cions for one nurseryman. You will only get Spitzenburghs and Newton, for I have nothing else.

MR. LAYRITZ—For all practical purposes, the far more important thing is the action of cions than the action of stocks; and for material results, too. A pear for a pear and the peach for the peach to be of any value whatever. By the selection of cions from a Spitzenburgh or the Newton Pippin, or the plum or any other fruit, it is in this way we may improve our fruit than by the stocks.


CybeRose note: At this time it was still common to confuse chimeras (e.g., Cytisus adami) with proper vegetative hybrids.

Stock / Scion Influence

Vegetative Hybrids