This section is from "The Horticulturist, And Journal Of Rural Art And Rural Taste", by P. Barry, A. J. Downing, J. Jay Smith, Peter B. Mead, F. W. Woodward, Henry T. Williams. Also available from Amazon: Horticulturist and Journal of Rural Art and Rural Taste.
Ik the preceding article we endeavored to establish that the vine presents unusual obstacles to cross fertilization. In the present, we shall give the evidence we promised, that hybridizing, though readily effected in certain exceptional and rare cases, is in general by no means an easy matter; and that when effected, the beauty and brilliancy of our greenhouses and flower gardens may be greatly increased; still the vinegrower or or-chardist can expect little benefit. We shall also at the same time endeavor to show why this process has been thus successful in the domains of Flora, while in those of Pomona "the efforts of the hybridizer are yet to be heard from," and in conclusion, touch upon the most successful method of originating new varieties of fruit.
I. As in the nature of things there are reasons why we should not expect fruitful hybrids to be numerous, for if man could without limit produce crosses, species and genera would soon be obliterated, and unlimited confusion supplant the present orderly arrangement of nature; so do we find in fact that hybrids are not common, while fruitful ones are still more rare. In the animal kingdom, no man's wealth will be much increased by the progeny of his mules. In the vegetable world, I for one do not expect our markets to be freely supplied with, or our goblets to overflow with, the juices of hybridized fruits. What is the testimony of those botanists who have made this subject a speciality? "The experiments of Kohlreuter on the hibiscus and cucurbitacm prove that there are certain species that cannot be crossed" (De Candolle. Veg. Physioiogie, p. 704.) " Many cases are recorded of nearly allied species refusing to intermix. Mr. Knight could not succeed in effecting a cross between the common and the Morello cherries," (species nearly allied, with blossoms convenient for operating,) and Dr. Lindley records his vain endeavors to cross the gooseberry and current.
Such plants as the apple and pear, the raspberry and blackberry, though very closely connected have not been known to intermix," (Lond. Horticultural Mag., quoted in Horticulturist, July, 1848.) " It might be expected that hybridization would be much more easy in dioecious than in hermaphrodite plants; the females, being more removed from the males, ought more readily to receive a strange pollen; but M. Lecoq remarks, that the observed facts seem contrary to this expectation, there being very few hybrids of dioecious plants; as if being more exposed to mixture they are protected by an organization more fixed which admits the action only of the pollen of its own species," (D. C. Veg. Phys. p. 705.) "These circumstances" (to wit, different species not blooming together - the necessity of the stamens of the plant acted on being removed, fertilization taking place under special integuments, and the preponderating influence of a plant's own pollen,) "render natural hybridization more rare than one thinks," (ibid, p 706.) "Hybrid fecundation in general is less perfect than natural. Gacrtner cites many proofs.
In cross fecundations made by him with the greatest care upon nineteen flowers of Nicotiana Langsdorfii, fertilized with N. Marylandica, and also in fourteen of the same fertilized with N. paniculata, only five succeeded. In nine of the same species, fertilized with N. quadrivalis, only one succeeded; in some cases, however, all succeeded," (ibid, 114.) The nicotiana, or tobacco tribe, by the by, is one of the easiest to cross. " The number of fertilized seeds in each fruit in cross fertilization is much less than in those which are natural; thus the papaver somniferum contains ordinarily two thousand seeds, crossed with the glaucium luteum, only six were found," (ibid).
Again; "Recent experiments have led to the following results: (1.) It is a much more difficult operation to produce hybrids even under every advantage than is usually supposed. The number of species capable of being impregnated even by skillful management, is very few; and in nature the stigma exerts a specific action which not only favors and quickens the operation of the pollen of its own species, but resists and retards that of another, so that the artist has not only to forestall the natural operation, but to experience opposition to his conducting the artificial one. (2.) Even when impregnation is effected, very few seeds are produced. Still fewer of these ripen; and fewest of all become healthy plants, capable of maintaining an independent existence. (3.) The offspring of a hybrid has never yet been known to possess a character foreign to those of its parents ; but it blends those of each, whence hybridization must be regarded as a means of obliterating, not creating, species. (4.) The offspring of hybrids are almost invariably barren, nor do we know of an authentic instance of the second generation maturing its seeds. (5.) In the animal kingdom, hybrids are still rarer in an artificial state ; are all but unknown in a natural one, and are almost invariably barren." (Hooker and Thompson's Flora Indica, quoted by A. Gray, in Silliman's Journal, January, 1856).
" With regard to the facility with which hybrids are produced, the prevalent opinions are extremely erroneous. Gaertner, the most recent and careful experimenter, who appears to have prosecuted his inquiries in a most philosophical spirit, says, that ten thousand experiments upon seven hundred species produced only two hundred and fifty true hybrids. It would have been most interesting had he added how many of these produced seeds ; how many of the latter were fertile, and for how many generations they were propagated." (J. D. Hooker's Flora of New Zealand, quoted in Silliman's Journal, vol. 17, new series, p. 335).
Finally, "Any continued effects of hybridization in uncontrolled nature seems to be thoroughly guarded against in two ways ; first, by the constitutional debility if not the invariable sterility of the hybrid offspring, rendering it of transient duration ; secondly, by the fact that when prolific at all, they usually become so through fertilization by one or the other of the parents when the offspring reverts to that specific type." (A. Gray, Silliman's Journal, 17, p. 344.) Such is the evidence that in general hybridizing is no easy matter. Whether the vine is a special exception I do not care just now further to discuss as with the present evidence my own opinion is unchanged. Five years will show, (with so many zealous experimenters in the field,) whether to hybridize it is in general a practicable thing, and whether such hybrids if obtained would be of any value. But these points I will not entirely pass over now.