CROSS-BREEDING, AND MULING OF PLANTS.
ISAAC ANDERSON HENRY
Hay Lodge, Trinity, Edinburgh.
IT is only recently that my attention was directed to your magazine for animadversions on an article I had written in a cotemporary, on the variegation in the leaves of plants; and having now possessed myself of the whole Numbers of your current volume, I have read with interest the very ably written articles of those who have so animadverted on the remarks I made, and also with still higher interest the doctrines of Mr. Beaton on the same subject. However much I lament to stand opposed to so eminent an authority as Mr. Beaton, whose vast experience and great powers of observation entitle his opinions to much respect; yet as he, and he only so far as I can see, maintains the belief and asserts it as doctrine not to be gainsayed that variegation is not disease, I do humbly demur to that assertion, and adhere to the views I adopted—that it is.
I cannot appeal like Mr. Beaton to the experience of forty years, but I can do so to at least half that term, during which time I have made no end of experiments which, if one-tenth of them had succeeded, would have gone far to establish the Lamarckian doctrine so recently revived by Mr. Darwin—that all plants now so diversified had their beginnings in a few original forms. How impressed with this belief I laboured to establish it, by trying to unite races and genera very distantly allied, I would now be ashamed to acknowledge in detail. But of this again.
How stands the question, and how stand opinions for variegation being health or disease?
The opinions of an "OLD SHOWMAN," which I generally endorsed by my own views, have been animadverted on as I have observed, not controverted by the other writers who give evidence, or offer remarks on the question.
"NICKERBOR" (why should men who write so well as "NICKERBOR," an "OLD SHOWMAN," or "G.," not give their names in full?) no doubt sets out holding with deference "that variegation is not disease;" and he cites the case of "the variegated Pelargonium Flower of the Day" not being a seedling, as an "OLD SHOWMAN" believed, but a sport, or if he will have it so, a diseased branch of a Scarlet Geranium whose history was known, and from which he, "NICKERBOR," once raised a batch of seedlings, every one of which "was variegated or diseased from the seed-lobes." This I can perfectly well understand. It is the common case of a diseased parent transmitting its taint to the progeny, of which we have instances every day as well in the animal as in the vegetable world. He next notices my own experiment of seedlings raised between the white-flowered and the scarlet-flowered Geraniums as adverse to my own views, and as tending to show that variegation is not disease. But may not disease be in the root as well as in the branch, in the seed as well as in the leaf? That is what I contend for, and I do think my experiment repeated, be it remembered, and with like results both times, proves it, and Mr. Beaton to this extent confirms the fact, that the disease or affection, for he disputes disease, is in the pollen. My white-flowered Pelargonium was the first of all its race I ever saw or heard of. It was given to me as a white-flowered variety of the common Scarlet Geranium, and I believed it to have been accidentally raised from seed, just as the Venus victrix, or first white-flowered Fuchsia was obtained; no one could tell how. But I do not know, and cannot vouch for its origin. If it was in itself, by whatever law, a departure from its kindred in the flower, might not a like departure be transmitted to the foliage of its progeny? Be this as it may, it certainly originated in the pollen—i.e., in the male, and not in the female parent; for when the cross was inverted, and the white-flowered kind made the seed-bearer, the healthy pollen of Tom Thumb was attested in the unbroken verdure of the seedlings, no malaffection ensuing from the taint or disease (supposing it present) in the seed-bearer. This is a fact, if it be not a law, worthy of being recorded, and I rejoice to be at one with Mr. Beaton upon it. But to proceed.
In this experiment "NICKERBOR" can maintain nothing against disease being the cause of variegation. I agree with him the result is remarkable.
I am not to dispute the indelible nature of variegation in some plants, though it is far from permanent in all, and I know of none where it is more fixed than in the Arundo donax, var. versicolor, or common Gardener's Garters, a plant whose variegation, I believe, no cultivation will eradicate. But it will be observed that this is set down by Loudon, I presume correctly, as a sport of 3 feet in height of the true Arundo donax, which he sets down as 10 feet high. Now, if this do not instruct disease in the striped variety, it establishes a great shortcoming in the vigour which characterises the non-variegated original species.
And this brings me to notice the very candid, and I think just comments offered by your other correspondent "G," who, though following suit to "NICKERBOR," frankly admits "one thing which may go far to support Mr. Anderson's views, and that is—that variegation is, I believe, invariably accompanied with a considerable diminution in vigour of growth." I do hold with "G." that this fact is invariable. Let any one look at a variegated plant, and compare it with its non-variegated congener, or with the leaves of a stray shoot (which may often be found on a variegated plant) having leaves of unvaried green, and compare their separate aspects, he will find the green tree or shoot possessed of a vigour and full development of leaf which are not in the variegated one. On going round our Botanic Garden here lately, with Mr. McNab, the curator, I observed a striking instance of this in a variegated Oak, a tree of some 10 feet or 12 feet high, and well spread on the top, no great dimensions for an Oak certainly, the leaves of which were all less or more attenuated, and as if nipped round the edges, the true outline being deficient in all of them. But amid the variegation, there arose a shoot or two of deep verdure, and here the leaves were entire, and about twice the size of the variegated ones. The case is common over all or most variegated plants, insomuch so, that but for the high authority arrayed against my views, or the views which I endorsed, I would have left the question to its fate, or its own solution.
But I must cite the testimony of no less a witness than Mr. Beaton himself to support my views. He tells us (page 312) what Mr. Standish has done, and can do among Rhododendrons in this way, that he can cross these, great and small, "down or up to the verge of variegation, and until there is not a particle of colour in the leaves, and no art of man can grow the seedlings; yet every one of them is in perfect health, according to its own degree of existence." Now this is just what I contend for. If Mr. Standish cannot get these blanched shoots to grow, it is just what I learned from his own lips not long since when he visited me here, and what my own experience taught me more than ten years ago, when I got some shoots entirely blanched among the variegated batch of crossed seedling Pelargoniums referred to, which, as they made no progress on the plant, I tried, but tried in vain, to strike as cuttings. Truly this looks very like disease. It is a pure albino, whose unhappy state in the human family, few, I presume, regard as anything but as diseased.
But I will not fall out with Mr. Beaton, "NICKERBOR," or "G." about names. We are all at one as to the main thing—that if it is not disease it is an affection of the plant entailing impaired vigour, and, I hold, diminished growth, whose true cause, whether originating in the seed or occurring in the branch, it is alike desirable to have ascertained; for there is at present a rage for these variegated things, and if the laws which produce or affect them can be clearly shown, then it will be profitable to some and instructive to all to know them.
I had gone on thus far when your new Part for August reached me, and there I found a much higher and more reliable evidence given to the same effect with my own in the excellent article by Dr. Morren, whose very searching investigations must settle the question thus far—that variegation is disease; for, after going over M. Sageret's conclusions, some of which may be exceptionable, he sums up by observing, "After this exposition of facts variegation may be regarded as a malady." The various causes assigned by M. Sageret—such as the seed being too old, imperfectly ripe, or defective in conformation, or that impregnation was imperfect by immature pollen, &c.—all necessarily infer that variegation is the result of disease, or imperfection of some sort in the seed, where it originates in the seedling. This very scientific paper must be held to close all further debate; yet the causes which produce such results are still a mystery, whose solution the practical physiologist has still to make out, the way to which certainly has been made less difficult by the facts and experiments communicated in the papers referred to.
paper will be found in the "Book of the Garden," pp. 319, 320, 321,
322; and the practical portion of it has been honoured with a place in
Professor Lindley's last edition of the "Theory of Horticulture," pp.
**I took this view in the article referred to ("Book of the Garden," vol. ii., page 319). Nature, as conjectured by Linnaeus, was occupied by but a few original types of the innumerable vegetable forms which bare been transmitted to us. How these few first types, if that great authority was right in that belief, have became varied and multiplied from classes to tribes, from tribes to genera, and from genera to species and endless varieties, belongs to those mysteries of Divine agency which set all inquiry at nought, and upon which it were equally unprofitable and presumptuous at the present time to speculate. For who, entreating of such a science, dare invade a field where the Omnipotent evoked no aid from man, ere yet, indeed, man was—while the sun, and skiey influences, and the whole host of insect races now extinct, were perhaps but parts of the agencies and instrumentalities by which
"With herbs, and plants, and fruitful trees,
The new-formed globe He crowned,"
and made it fit for man's use and habitation! Who can speculate now on these, or those atmospheric properties, instinct with life, under whose influence nun grew and increased in strength till the span of man's existence extended to near a thousand years—when there were giants on the earth—
"When man was in stature as towers in our time.
The firstborn of Nature, and, like her, sublime,"
—a life-giving and a life-sustaining Spirit breathed the will and effected the purposes of the the creator? Perhaps a larger portion and a more genial form of electricity than now obtains may have imparted a principle of higher vitality to the air, and through that medium have communicated a stronger impulse and more enduring energies to both animal and vegetable life. This may or may not have been; certain it is that a change has taken place. Since the Deluge the vital forces have been greatly weakened. Man since then has scarce lived a tithe of his former term; and the vast exhumation of fossil flora bespeak an exuberance and variety of vegetation in temperate zones that have no parallel at the present day even in tropical regions.
I had intended, ere I concluded this paper, to have gone a little into the subject of all-engrossing interest of hybridising and cross-breeding of plants, upon which Mr. Beaton in his recent papers has thrown much light and communicated many facts known to few if any before. But though I cannot now go into the subject, I may take it up at a future time, and state some results of my own manifold experiences in this way; by many of which I will corroborate Mr. Beaton, though, on the whole, what I hare made out warrant me in expecting much stranger things to be accomplished "than have been dreamt of in his philosophy." Few take into account the possibility of doing at one time what they have failed to do at another, and so abandon in disgust experiments which may have oft before led only to disappointment. The patient experimentalist must wait weeks and months for a favourable time. In my article in Mr. M'lntosh's "Book of the Garden,"* I insisted upon this being studiously watched for and improved. All my subsequent experience confirms me more and more in that view. Few such days as I considered fit for hybridising (not merely crossing), occurred in this bygone summer, and scarcely any in the summer of lest year. Many things all but given up as hopeless I would resume on an auspicious day (which in this climate are truly like angels' visits)—a day not of strong but of subdued sunlight, with a sky so charged with electricity as to give a buoyancy to the spirits and elasticity to the limbs—a day when man, and bird, and beast are in their most joyous mood—seize such a day and shun "the short anthers;" and Darwin himself might yet take heart of grace and do something to sustain his own doctrines. These doctrines I long clung to, and gave up only after hundreds of failures. But I gave expression to one view in the paper above referred to—in the "Book of the Garden," vol. ii., page 320, which I think has not been fully if at all regarded by Mr. Darwin or any other naturalist bearing closely on the subject of these inquiries—namely, the gaps, some greater and some smaller, which occur between various orders of plants. May there not have been, ere this globe suffered from so many disruptions, an affinity between plant and plant, which, by the losses these convulsions occasioned, is now also broken up and so creating these gulfs between which have given rise to races, genera, and species of all the various dissimilar forms we see around us? May there not, too, have been, in the early stages of this world's history, a very different state of atmospheric properties from what now obtains more favourable to the ends in question?**
Having already trespassed on your space so far, I must now draw to a close. Ere I do so, however, I must congratulate and compliment Mr. Beaton on his discovery about the "short anthers." At page 312 of your first volume he observes, "In the great bulk of Scarlet and Horseshoe Geraniums there are but seven stamens, four long ones, one of medium length, but which is often wanting, and two almost sessile like the anthers of Wheat—that is, very short indeed, and opening at the bottom face to face. These two are they which reduce a whole family to beggars—first to dwarfs or Tom Thumbs, or, better still, to Minimums," &c. I cannot express how much I was taken by surprise by this remarkable enunciation; for I had from time to time, for ten years past or more, been drawn to consider the purposes of these short stamens in the races of the Rhododendron, and wrought with them till I produced the very results Mr. Beaton has observed.
The Rhododendron Edgworthi had no sooner delighted cultivators with its lovely, large, sweet-scented flowers, than the desire became general to transfer its rare properties into a dwarfer progeny. And many, unhappily, for this purpose began their operations by attempting crosses on this species. The results were a disappointment; for where seeds were produced the progeny were found, I believe in some cases only after many years, to be pure Edgworthi, native pollen having, perhaps, by means of insects superseded the foreign application. I fortunately started on the proper track, and made the crosses with its pollen on the other species. But it may be proper and interesting in passing here to mention, that though I have often subsequently tried to make the cross upon Edgworthi, I never succeeded in getting seeds from any cross so attempted upon that most untractable species.
I began my operations on another pure species of Dr. Hooker's introduction—viz., R. ciliatum, both being from the Sikkim ranges of the Himalaya, the latter having all the fine dwarf habit, the absence of which is the great fault of Edgworthi, a straggling, ungainly thing. Well, to work I went, and as my great aim was to make the progeny as puny as possible, I purposely used the two short anthers which Mr. Beaton refers to. But I used long as well as short stamens. These crosses, which were effected in the spring of 1855, took, and I sowed the seeds in September and October of that year. There were five separate batches, marked A, B, C, &c. Now, of the taller-growing kinds, I have two plants set with flower-buds. But these were a set of dwarfs, which, with all my care never raised their heads above the pots, and these, so far as they are now living, creep along with small tufts of foliage on the surface of the pots, pretty enough in their way, but without showing the least appearance of bud or blossom. Through the six years of their existence the tallest have got shifted; but I have no doubt they are the pigmy progeny of the short stamens.
Mr. Beaton as the first, perhaps, to find out, and certainly the first so far as I know, to announce this strange discovery, is entitled to its full merit. Its full value has not yet been sufficiently tested. For although I have produced the tiny things in the Rhododendron family which he has done with Pelargonium, inquiry should not stop here. And for my part I did not limit my aim merely to produce by them more dwarfish plants than the parents. Regarding as I did, the pollen of these small anthers as of finer particles than the pollen of the longer and larger ones, I used it as a provision of Nature's own suggesting, in preference to the latter in crossing the smaller species whose pollen-tubes I feared might not admit the grosser globules of these larger anthers. And when the two dwarf stamens failed, I used the smallest and shortest of the remaining stamens. I still cling to the belief that in this way I effected crosses in which with larger anthers I should have failed. I look on them as affording the chance of effecting unions with remote species or genera—as the links, in short, by which large and family groups might he united. These were in the days of my Lamarckian notions; and the recoil consequent on the failure of the fanciful theories I then indulged, discouraged me from pursuing or even recording the results of my experiments with them. I did wrong in this, and fresh trials ought yet to be made; and though these odd pair of tiny stamens are peculiar, perhaps, to the Pelargonia and Rhododendra, yet stamens analogous whose pollen possesses like properties, may be found in other races. The experimenter should go bit by bit, and never despise the day of small things, and if he cannot produce a mule between a Raspberry and a Strawberry, or a Currant and a Gooseberry (I never tried the latter), let him try the muling of more nearly allied things. I do not despair yet of producing a mule between the Blackberry and Raspberry. I made the effort this past summer, but my experiment was marred by an accident. I certainly did try for a mule between the Rubus ideaus and the Strawberry, and the latter with Rubus glabratus, an Andean species which I alone possess, from both of which crosses I have young plants, the Strawberry being the seed-bearer in both. Though the seedlings are dissimilar to look at, I cannot vouch as yet for the crosses being true. I have a plant of the former cross, now three years old, which has never yet fruited. The leaves often divide into four instead of three lobes, and the footstalks are much more wiry or shrubby than the Strawberry. Here Myatt's Pine was the seed-bearer. There seems evidently a variation from the female parent, and though, certainly, it is most like the Strawberry, there is little disposition to throw off runners. My other crosses in these tribes being of this summer, the seedlings are too young to hazard any opinion about them.
These trials may suggest similar experiments to others. This is not a field where any one can assign a definite limit beyond which, in some favourable season, another may not go, and none should be discouraged by another's failure. Neither should the bold experimentalist follow suit to the most enlightened. As the most valuable discoveries in medicine have been made by those whom the faculty call quacks, so may like success await those who here adventure somewhat on their own inventions. Yet let them not go to far extremes, else failure and vexation will inevitably be the fruit of their labours.—ISAAC ANDERSON HENRY, Hay Lodge, Trinity, Edinburgh.