Transactions of the Horticultural Society 4: 367-373 (1822)
LIII. Observations on Hybrids.
By THOMAS ANDREW KNIGHT, Esq. F. R. S. &c. President.

Read February 6th, 1821.

* The early period at which the Apricot unfolds its flowers leads me to believe it to be a native of a cold climate: and I suspect the French word Abricot, the English Apricock, and the African Berrikokka to have been alike derived from the Latin word Praecocia, which the Romans (there is every reason to believe) pronounced Praikokia, and which was the term applied to early varieties of Peaches, which probably included the Apricot. The Greeks also wrote the Latin word, as I suppose the Romans to have pronounced it, Πρακοκια. Hardouin's Edition of Pliny, Lib. 15. Sec. XI
+ See Horticultural Transactions, vol. iii. Appendix, page 23.

MUCH difference of opinion appears to exist between my friend the Hon. WILLIAM HERBERT, and myself, relatively to the production of Hybrid Plants, he supposing that many originally distinct species are capable of breeding together, without producing mules (that is, without producing plants incapable of affording offspring), and I considering the fact of two supposed species having bred together, without producing mules, to be evidence of the original specific identity of the two. Our difference of opinion is, however, I believe, apparently much greater than it really is: for I readily concede to Mr. HERBERT, that great numbers, perhaps more than half, of the species enumerated by botanical writers, may be made to breed together, with greater or less degrees of facility: but upon what sufficient evidence the originally specific diversity of these rests, I have never been able to obtain any thing like satisfactory information; and I cannot by any means admit, that plants ought to be considered of originally distinct species, merely because they happen to be found to have assumed somewhat different forms, or colours, in an uncultivated state. The Genus Prunus contains the P. Armeniaca, P. Cerasus, P. domestica, P. insititia, P. spinosa, P. Sibirica, and many others. Of these, I feel perfectly confident, that no art will ever obtain offspring (not being mules) between the Prunus Armeniaca, P. Cerasus, and P. domestica: but I do not entertain much doubt of being able to obtain an endless variety of perfect offspring between the P. domestica, P. insititia, and P. spinosa; and still less doubt of obtaining an abundant variety of offspring from the P. Armeniaca and P. Sibirica. The former, the common Apricot, is found, according to M. REGNIER, (for a translation of whose account, we are indebted to Mr. SALISBURY),+ in a wild state in the Oases of Africa. It is there a rich and sweet fruit, of a yellow colour. The fruit of the P. Sibirica, seeds of which came to me last year from Dr. FISCHER of Gorinki is, on the contrary, I understand, black, very acid, and of small size: but nevertheless, if these apparently distinct species will breed together, and I confidently expect they will, without giving existence to mule plants, I shall not hesitate to pronounce these plants of one and the same species; as I have done relatively to the Scarlet, the Pine, and Chili Strawberries. Botanists may nevertheless, if they please, continue to call these transmutable plants, Species; but if they do so, I think they should find some other term for such species as are not transmutable; and which will either not breed together at all, or which, breeding together, give existence to mule plants. I do not, however, feel any anxiety, or wish, to defend my own hypothetical opinions upon this subject: on the contrary, I shall be most happy to see them proved to be erroneous; and my chief object in addressing the present communication to the Horticultural Society is to point out a circumstance which is more favourable to Mr. HERBERT'S opinions, than any other which has come under my observations.

* Since the foregoing observations were addressed to the Horticultural Society, a tree which sprang from a seed of a Sweet Almond and pollen of the early Violet Nectarine, has produced a profusion of perfectly well organized blossoms, with abundant pollen; after having, in the three preceding years, afforded imperfect blossoms only. If such pollen prove efficient, which I see no reason to doubt, either the specific identity of the Peach and Almond, or the transmutability of the two species, will be proved. But if the Peach be an originally distinct species, where could it have lain concealed from the creation to the reign of Claudius Caesar?

I sent to the Society, some years ago, a fruit which sprang from a seed of a Sweet Almond and the pollen of a Peach blossom, and which in every respect presented the character of a perfectly melting Peach. When the tree, which afforded that fruit, first produced blossoms, I introduced into them the pollen of another Peach tree, with the view of obtaining more improved varieties of the Peach of this family: and the necessary preparation of such blossoms prevented my noticing an imperfection, which I have since observed in them. Little or no pollen is ever produced in them; and though the tree has borne well subsequently, upon the open wall, and has produced perfect seeds without any particular attention having been paid to it, I suspect that its blossoms have been fecundated by those of some adjoining Nectarine trees. Having, however, often observed, that varieties of the same acknowledged identical species, when one was in a highly cultivated, and the other in a perfectly wild state, did not readily succeed, when grafted upon each other, owing, probably, to the very different qualities of their circulating fluids, I conceived it possible that the same causes might have prevented a perfect union at once taking place between the Almond and Peach tree. I therefore waited till I had an opportunity of observing, in the last summer, the blossoms of a second generation, which proved in every respect, as imperfect as those of the first tree, and like those, afforded fruit and perfect seeds with the pollen of an adjoining Nectarine tree. This result, which I did not anticipate, appears interesting: but I hesitate in drawing, at present, any inferences from it.*

The vegetable and animal worlds present so much similarity in almost every thing which respects the generation of offspring, that the extent to which mules are permitted to exist in the animal world, might have been expected to point out the utmost limits of their existence amongst plants; for every animal is driven by its instinctive feelings to seek its proper mate, whilst an unrestrained and unlimited intercourse between plants is carried on by the incidental operation of winds and insects. But if the fruit tree obtained from the Almond and pollen of the Peach be a mule, nature has already permitted it to propagate offspring to an extent scarcely, if at all, known in the animal world. I have, however, heard it asserted, that female mule birds have been known to breed under similar circumstances; that is, with a male of the same species as the male parent of the mule: but upon trying the experiment, it did not at all succeed in my hands. The mule birds laid eggs, apparently well organised, upon which they sat; but the eggs soon became putrid; and I had good reason to believe, that the first pulse of life had never beaten in any of them.

If hybrid plants had been formed as abundantly as LINNAEUS and some of his followers have imagined, and such had proved capable of affording offspring, all traces of genus and species must surely, long ago have been lost and obliterated; for the seed vessel even of a monogynous blossom often affords plants which are obviously the offspring of different male parents; and I believe I could adduce many facts, which would satisfactorily prove, that a single plant is often the offspring of more than one, and, in some instances, of many male parents. Under such circumstances every species of plant which, either in a natural state, or cultivated by man, has been once made to sport in varieties, must almost of necessity continue to assume variations of form. Some of these have often been found to resemble other species of the same genus, or other varieties of the same species, and of permanent habits, which were assumed to be species; but I have never yet seen a hybrid plant, capable of affording offspring, which had been proved, by any thing like satisfactory evidence, to have sprung from two originally distinct species; and I must therefore continue to believe, that no species capable of propagating offspring, either of plant or animal, now exists, which did not come as such immediately from the hand of the Creator.

Having spoken, in the preceding account, of mule birds, I will take this opportunity of recording a very singular circumstance, which came under my observation, whilst I was engaged in the experiments which I have stated. A person informed me that a farmer, who resided a few miles distant from me, possessed a mule bird, which was bred between the common hen, and the wood-pigeon; and which my informant had seen, and described with accuracy; I took, in consequence, the earliest opportunity of seeing the farmer, and the supposed mule bird; because I thought that nature had strictly prohibited the production of mules between species so distinct, and had usually made the death of the female the price of the attempt. The information I obtained was, that the children in his house (his infant brothers and sisters), had reared a young wood-pigeon and a motherless chicken together; that these became much attached to each other, and appeared to have paired, the wood-pigeon constantly paying court to the young hen, as he would have done to a female of his own species. The hen subsequently laid eleven eggs, which she sat upon, and produced one offspring, the bird in question. It was wholly without comb, and it had soft turgid nostrils, extremely similar to those of a wood-pigeon; and the whole profile of its head, exclusive of the point of the beak, bore a most striking resemblance to that of its supposed male parent. It, however, certainly was not the offspring of a wood-pigeon, nor a mule; for it bred freely. I ought to have preserved the bird, which was offered me, and, perhaps I convict myself of an act of unpardonable stupidity in not having done so. But it was a great favourite with the children who possessed it; and I did not like to deprive them of it. The animal physiologist will draw his own conclusions respecting these singular facts; 1 do not feel qualified to give an opinion.