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.
I should have preferred waiting until it was again in blossom before discussing farther the practicability of hybridizing the vine, as, with its floral organs before them, your readers could then decide for themselves as to the difficulty or ease with which it could be effected. But as some interest seems to be felt in the matter, I will state more fully my views, which they can verify, if correct, at that time. Meanwhile, those of them that have access to the article " Botany" in the new edition of the Encyclopaedia Britannica, or to Gray's Botanical Text-Book, can get a very good idea of the structure of the vine blossom from the enlarged figures there given.
That the vine cannot be hybridized, is of course like any other negative proposition, scarcely possible to be proved; and that it is nearly impossible, is nearly as difficult to establish. It will perhaps not be so difficult to make evident, that if Mr. Rogers, as appears from your last issue, has succeeded in this, he has been very fortunate; that if these vines produced (being true hybrids), and set their fruit well, and seed freely, it is remarkable; and should their fruit prove valuable, and they be brought into general cultivation, it will be the first instance of the kind in history, and I for one congratulate him on his success, if he has really succeeded.
The question is not one of cross-breeding merely, or the fertilization of one variety by the pollen of another variety of the same species (itself a difficult matter in the vine, as I think), but the intermixture of species themselves. Whatever success Knight had in his experiments, was not in hybridizing, but in cross-breeding. The only hybrid fruit that I remember, was his almond peach, which was good for nothing.
The controverted point in the report of the Georgia Committee is the observation of Le Conte: "Although, among some families of plants, hybrids occur naturally, or may be formed artificially, yet it is difficult to understand how this can ever be the case in the genus Vitis. In forming a hybrid, it is necessary to emasculate the flower we wish to produce fruit, and to impregnate its pistil with the pollen of some other species. This is impossible in the present instance, on account of the minuteness of the flower and its parts of fructification," together with the additional remark of the Committee: "Nor is this all. He might have added another difficulty. The petals are caducous, and cohere at their tips, forming a little cap, which, in the act of falling off whole, draws over from one side or the other, almost invariably, the pollen from its own stamens upon the pistil. The chances then are that the operator on so minute a flower, in the act of removing this cap, and then the stamens, would already have fertilized the pistil before applying the pollen of the species or variety selected.
We would not, however, assert that hybridization, naturally or artificially, is absolutely impossible, but nearly so," etc.
It is true, this cap is easily removed. Dr. C. W. Grant informs me that he has also found no great difficulty in taking out the stamens, or in applying the pollen, which he has done repeatedly; but the operation succeeded only so far as to render the action of its own pollen abortive. The florets operated upon produced no fruit, and the cause of this sterility lies undoubtedly in the parts of the floret being so minute that he could not remove the stamens without injury to the stigma. Indeed, the minuteness of the parts may be judged from this: After we had noticed that the species rotundifolia was six-petalled, it required close scrutiny with good eyes to determine whether there were really six stamens or but five, without separating them; and where the eye can scarcely distinguish, it is difficult, certainly, for the hand to manipulate.
Another difficulty in hybridization is, that the blossoms of the foreign grapes (at least with us) open much earlier than our native species; but this is not insuperable, as the pollen may be kept some time.
But, after all, when the whole manipulation has been performed, the pollen applied, and when fertilization follows, there is no certainty that there has been a true cross. Gaertner, the best authority on hybridization as far as observation on experiment could qualify one, says that, in any plant, " the influence of its own pollen is so preponderant over even that of a great mass of foreign pollen, that a microscopic quantity of its own can annihilate that of the other." Again: "The fact" (says De Candolle, Veg. Physiologic, p. 105) "which the experiments of Kohlreuter have best demonstrated is, that the smallest quantity of pollen is sufficient for fecundation. Hence arises one of the great difficulties of hybridizing, as when a stigma has been acted upon by its own pollen, it is not susceptible of being fertilized by another species." The same author also states (page 479) that "in many genera, fecundation executes itself in the unexpanded bud, or at the moment of expansion, or in the shelter of certain special integuments, as the cohering petals of the vine." Let it at the same time, in this connection, be remembered that when the stigma of any floret is in a fit state to receive the pollen of another species, its own pollen is also in a fit state to fertilize it.
Bearing the above facts in mind, I for one do not feel inclined to change my opinion, already expressed, that "the chances then are that an operation on so minute a flower," or one where the parts are so near each other, "in the act of removing this cap, and then the stamens, would have already fertilized the pistil," etc. Mr. Rogers made his experiments "when the blossoms on the native vine had begun to open;" then " a few clusters were selected on which to operate from those most forward, and nearly ready to open." If the operation was so carefully performed as not to injure the stigma, it is probable that, in any ordinary vine, it would have been self-fertilized; but as, in this variety, only from four to eight berries are found ordinarily to set, it is probable he was so fortunate as to happen upon a variety in which the anthers are frequently or generally imperfect in most of the florets, while the stigma was in its normal condition. Such being the case, those in which the anthers were perfect probably did not hybridize, and of course showed the native leaf in the seedling produced, while, with a portion, 1 am inclined to think a cross of species was effected, especially as the process seems to have been conducted with extraordinary care.
There then may have been an exceptional case, but we are confident that every one of the readers of the Horticulturist will, after examining the florets of the vine for themselves, agree that it presents unusual obstacles to the hybridizer.
That hybridizing, in general, is of itself no easy matter, we shall show in another article.