Book of the Garden pp. 319-322 (1855)
For the following remarks on this very interesting subject we are indebted to our excellent friend Isaac Anderson, Esq., S.S.C., one of the most scientific, energetic, and successful hybridisers of the present day:—
"To go fully into the theory and practice of hybridising, a volume might be devoted to the subject, and still leave it unexhausted. To start with the beginning would be to start with creation itself—in fact, nature, as conjectured by Linnaeus, was occupied by but few original types of the innumerable vegetable forms which have been transmitted to us. How these few first types, if that great authority was right in that belief, have become 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, in treating of such a science, dare invade a field where the Omnipotent invoked no aid from man —ere yet, indeed, man was; while the sun and skyey influences, and the whole host of insectivorous races, now extinct, were perhaps but parts of the agencies and instrumentalities by which,
and plants, and fruitful trees,
The now-formed globe He crowned,'
and made it fit for man's use and habitation? Who can speculate now on those atmospheric properties, 'instinct with life,' under whose influence man grew and increased in strength, till the span of his existence extended to near a thousand years—when there were giants on the earth—
man was in stature as tow'rs in our time,
The first-born of Nature, and, like her, sublime?'
A life-giving and life-sustaining Spirit breathed the will, and effected the purposes of 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 exhumations 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.
"Why do we now see natural families with genera whose affinities are indisputable, and yet in their extreme links so dissimilar? Perhaps no one of the larger family of plants has its intermediate connections better filled up than the Ericaceae, yet how many links are awanting in the chain between the Rhododendron arboreum of India, of 40 feet high, and the Chamaeledon (Azalea) procumbens of our own Highland mountains, of only 4 inches, or some of the smaller heaths! Though all allied, how many links are there between the various tribes, and even genera, of this most interesting family; e. g., between the Vaccinieae and the Pyroleae as separate tribes, or between the Rhododendron and the Menziesia, as separate genera. The scarcely-known elevated plateaus and ridges of the Andes have already yielded up some kindred races in the Bejaria and Thibaudia; and who can tell if, when better explored, many more links awanting may not be supplied? Travellers have observed examples of the Rhodoreae on the high mountains of the Hawaian group of isles in the Pacific, and in Manilla, Malacca, and other islands of the Indian Ocean, as well as in North-west America, yet unknown to gardens. Thirteen species of this family have been observed on one hill in Borneo alone, and at least half that number in Java. Dr Hooker has reclaimed about thirty species from the Sikkim ranges of the Himalaya, and of such varied growth and aspect, that our thymes may represent the one group, and our oaks the other— one tiny thing (R. nivale) creeping on the ground at 18,000 feet above the sea, and another (R. barbatum) attaining a stature of 60 feet.
"All these discoveries have done much to fill up many gaps in this widely-distributed family, and the discoveries of future travellers may fill up many more.
"But how many tribes, genera, and their species, are for ever lost! Man inhabits but the disjecta membra of a former world. With continents, now beneath the ocean, are buried— perhaps for ever lost—genera which, if restored, might supply all those gaps which leave existing races so wide apart. But nature has left materials to work upon, and the art and ingenuity of man may do much to fill up the blanks.
"A very eminent nurseryman—the late Mr Cunningham of Comely Bank—so far filled up one link of this order, by hybridising the Phyllodoce (Menziesia) caerulea with the Rhodothamnus chamaecistus, and producing therefrom the beautiful (so-called) Brianthus erectus. But the parents were too far remote, and the progeny— a proper mule—is consequently barren. It is somewhat singular, that while the M. caerulea will cross with the Rhodothamnus chamaecistus, the latter will not be crossed with it. It was the Menziesia that bore the seed from which the so-called Brianthus was raised. I speak from my own experience in this matter, having, before Mr Cunningham's experiment was known, attempted unsuccessfully to cross the Rhodothamnus with the M. Caerulea, though I have since succeeded in ripening seeds and raising plants from the cross inverted. These I sowed on 18th June 1850, and on 10th September four young plants had come through.
"To those who would attempt the hybridising or cross-breeding of plants, I will now offer some suggestions for their guidance.
"It is an essential element to success that the operator be possessed of indomitable patience, watchfulness, and perseverance. Having determined on the subjects on which he is to operate, if the plants are in the open ground, he will have them put into pots, and removed under glass, so as to escape the accidents of variable temperature—of wind, rain, and dust, and, above all, of insects. A greenhouse fully exposed to the sun is best adapted for the purpose, at least as regards hardy and proper greenhouse plants.
"Having got them housed, secure a comer where they are least likely to be visited by bees or other insects. The plants which are to yield the pollen, and the plants which are to bear the seed, should be both kept in the same temperature; but where this cannot be managed, pollen from an outside plant, in genial summer weather, may be used, provided it can be got: for there is a class of insects which live exclusively on pollen, and devour it so fast after the pollen vessels open, that, unless the plant in under a hand-glass (which I would recommend), it is scarcely possible to get any pollen for the required purpose. To secure against chances of this nature, a sprig with opening bloom may be token and kept in a phial and water inside, where it will get sufficient sun to ripen the pollen. But here, too, insects must be watched, and destroyed if they intrude. An insect like, but smaller, than the common hive bee, which flits about by fits and starts, on expanded wings, after the manner of the dragon-fly, is the greatest pest, and seems to feed exclusively on pollen. The hive bee, the humble bee, and wasp give the next greatest annoyance. All these may be excluded by netting fixed over apertures from open sashes or the like. Too much care cannot be bestowed on excluding these intruders, whose single touch, in many cases, might neutralise the intended result; for the slightest application of pollen native to the parent plant is said by physiologists to supersede all foreign agency, unless, perhaps, in the crossing of mere varieties; and the truth of this observation consists with my own experience. Without due precaution now, the labour, anxiety, and watchfulness of years may issue in vexation and disappointment.
"As a further precaution still, and to prevent self-fertilisation, divest the blooms to be operated on not only of their anthers, but also of their corollas. Remove also all contiguous blooms upon the plant, lest the syringe incautiously directed, or some sudden draft of air, convey the native pollen, and anticipate the intended operation. The corolla appears to be the means by which insects are attracted; and though, when it is removed, the honey on which they feed is still present, they seem puzzled or indifferent about collecting it; or if, haply, they should alight on the dismantled flower (which I never have detected), the stigma is in most cases safe from their contact.
"It will be some days—probably a week or more, if the weather be not sunny—ere the stigma is in a fit condition for fertilisation. This is indicated in many families, such as ericaceae, rosaceae, scrophularineae, aurantiaceae, &c., by a viscous exudation in the sutures (where these exist) of the stigma, but generally covering the entire surface of that organ. In this condition the stigma may remain many days, during which fertilisation may be performed; and this period will be longer or shorter as the weather is sunny, or damp or overcast.
"In certain families, such as the Malvaceae, Geraniaceae, &c., where the stigma divides itself into feathery parts, and where the viscous process is either absent or inappreciable by the eye, the separation of these parts, the bursting of the pollen, the maturity of the stigma, and all which a little experience will detect, indicate the proper time for the operation, sunny or cloudy weather always affecting the duration of the period during which it may be successfully performed.
"As to the proper time and season best adapted for such experiments, a treatise might be written; but here a few remarks must suffice.
"As for the season of the year, from early spring to midsummer I would account the best period; but, as I have just observed, I regard all cold, damp, cloudy, and ungenial weather as unfavourable. On the other hand, when the weather is genial, not so much from sun heat as at times occurs from the atmosphere being moderately charged with electricity, when there is an elasticity, so to speak, in the balmy air, and all nature seems joyous and instinct with life, this, of all others, is the season which the hybridist should improve, and above all if he attempt muling.
"The hybridist should be provided with a pocket lent, a pair of wire pincers, and various coloured silk threads.
"With the lens he will observe the maturity of the pollen and the condition of the stigma, whether the former has attained its powdery, and the latter (if such is its nature) its viscous condition. If he find both the pollen and the stigma in a fit state, he will, with the pincers, apply an anther with ripened pollen, and by the gentlest touch distribute it very thinly over the summit of the stigma. The operation performed, he will mark it by tying round the flower-stalk a bit of that particular coloured silk thread which he wishes to indicate the particular plant which bore the pollen, and at same time tie a bit of the same silk round the stem of the latter, which will serve till recorded in a note-book, which (should be kept by every one trying experiments on a large scale.
"It would be out of place here to give even a general outline of the parts of flowers, to show how these differ the one from the other in various tribes of plants. The experimenter, if he is not a botanist, and even though he is partially acquainted with the science, must, from books and observation, make himself familiar with the various organs, male and female, of each separate family of plants on which he means to work, otherwise he will be often puzzled where to find them, or even to distinguish the one from the other.
"As for the time of the day, it may be done almost any hour from 9 A.m. till 4 o'clock P.M., and with equal success. My other avocations have often limited me to earlier and later hours; but I would suggest from ten till two o'clock as the best time of day, always preferring fair, genial, and sunny, to chill, damp, or cloudy days.
"On recurring to my note-book for 1850,1 find a very favourable state of atmosphere occurred in the beginning of March of that year, when I crossed the Phyllodoce (Menziesia) caerulea with the Rhodothamnus (Rhododendron) chamaecistus, sowed on 18th June that year, as above noticed. At this time, too, I succeeded in crossing the above rhodothamnus with a large-leaved white-flowered Nepal species of rhododendron, the blooms of which were 2 inches across the limb. But though I ripened that season three or four pods of this last cross, each pod of seed beautifully ripened, all of which I sowed, I cannot assert that any one seed vegetated; and though it is now nearly three years since the seeds were sown, I
still preserve the seed-pot. And I may remark here, from my own experience, that two years is not too soon to despair of vegetation even of seeds from abroad, on which, of course, no cross had been effected.
"Few seasons have occurred so favourable for the hybridist as the short interval in the beginning of March 1850, above alluded to. Singularly enough, happening to visit Lord Rosslyn's gardens at Dysart House, on the 1st of June that year, with the late Professor Dunbar, Mr M'lntosh (the author), and Mr Sprott, I observed the above rhodothamnus marked as crossed. I found it had been crossed at the above period, and with Rhododendron arboreum! The seed-pods were then fully swollen, and approaching maturity; but I have not heard that anything has come of them.
"It is quite unnecessary to offer any directions as to the results to be effected. If it is desired to reproduce the larger, finer formed, or higher coloured bloom of a plant having a tall, straggling, or too robust a growth, or having too large or too coarse foliage in a plant without these drawbacks, I need not suggest to select, in another species of the same family, a plant of an opposite character and properties—say of dwarf compact growth, handsome foliage, and free flowering habit; and if such can be obtained, work with it, making the latter the seed-bearer. Or, if it be desirable to impart the fragrance of a less handsome kind to another more handsome, I would make the cross upon the latter. I cannot speak with certainty from my own experiments how far perfume may be so communicated; but I have some things far advanced to maturity to test it; and I entertain the hope that fragrance may not only be so imparted, but even heightened, varied, and improved. Or if it be desired to transfer all, or any valuable property or quality, from a tender exotic species to a native or hardy kind, work upon the latter; for so far as constitution goes, I agree with those who hold that the female overrules in this particular. I would offer this caution to those who wish to preserve the purity of certain flowers for exhibition, especially those having white grounds, not to cross such with high-coloured sorts. I once spoiled a pure white bloomed Calceolaria for exhibition by crossing it with a crimson sort; all the blooms on those branches where the operation had been performed, being stained red, and not the few flowers merely on which the cross was effected.
"In this note, already too long, I cannot further illustrate my remarks, by recorded experiments in the various tribes upon which 1 have tried my hand; but I cannot leave the subject without inculcating, in the strongest manner, the observance of the rules I have laid down to prevent vexatious disappointments. If any doubts arise about the cross being genuine or effectually secured, let not the seeds be sown. Three, four, five, and even six years, must oftentimes elapse with trees and shrubby things ere the result can be judged of; and if eventually it prove a failure, or even doubtful, it is worse than labour lost, inasmuch as it may mislead. If there is no great departure from the female parent, the issue is to be mistrusted. It is singular, if well accomplished, how much of both parents is blended in the progeny. Gentlemen eminent as physiologists have read nature's laws in these matters a little differently from what my own humble experience has taught me, and assigned to the progeny the constitution and general aspect of the one parent, while they gave the inflorescence and fruit to the other. I have crossed and inverted the cross, and can venture to give no evidence on the point, except, perhaps, as to constitution, to which the seed-bearer, I think, contributes most. A well-managed hybrid should and will blend both parents into a distinct intermediate, insomuch so as to produce often what might pass for a new species. If the leaning be to one more than another, it is probably to the female, though this will not always be the case.
"Again, it is asserted that a proper hybrid— i. e., one species which is crossed with another species, which is separate and distinct from it—will produce no fertile seeds. This does not accord with my observations. Dr Lindley has remarked very justly ('Theory of Horticulture,' p. 69), 'But facts prove that undoubted hybrids may be fertile.' My hybrid, Veronica Balfouriana (an intermediate between V. saxatilis and V. fruticulosa), seeds, I would say, more abundantly than either parent; and the progeny from its self-sown seeds I find to be of various shades of blue, violet, and red, rising in my garden, some having actually larger, finer, and higher-coloured blooms than the parent bearing the seed; and I am familiar with the same result in other things. Yet I am far from asserting fertility in the produce between two members of allied but distinct genera—such, for example, as in the Brianthus, which I have found to be unproductive, whether employed as the male or female parent. As above conjectured, its parents were far too remote in nature's own arrangement. The hybridist has a field before him ever suggestive of new modes of acting. He may try, as I have done, what may be effected under various tinted glass. My persuasion is, that I effected from a pale yellow a pure white-grounded calceolaria, by placing the plants under blue-shaded glass, by which the sun's rays wore much subdued. He may also apply chemical solutions to plants with ripening seeds. Nature, in producing, as it sometimes does, plants with blooms of colours opposite to those of the parent, must be governed by some law. Why may not this law be found out? For example, under what influences was the first white fuchsia, the F. Venus Victrix, produced, the purest yet of all the race, and the source from which all the whites have been derived?
"While I have necessarily confined the above remarks to things proper to the flower-garden, a wide and still more important field lies beyond. The late lamented Mr Knight of Downtown did much in this way to improve our garden fruits and other esculents, and with a success that none else—so far as I am aware— has since attained. Why should not these efforts be extended to the improvement of agricultural as well as horticultural productions? Why not carry them into field and forest, to the creation of new, more useful, and more elegant forms? Nature is boundless, and its objects are endless, and this subject, of all others connected with plants, the most engrossing and exciting. Rich results await the intelligent experimenter; but I would advise none to embark in the pursuit who has not sufficient leisure to devote to it, and, as I said before, who is not possessed of indomitable patience, watchfulness, and perseverance, with a fixed determination not to be fretted or discouraged by frequent failures.
"MARYFIELD, June 1853. I. A."