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.
It will have been seen by a communication in our last number, that experimentalists are puzzled to understand how it is possible to make two embryos grow together by grafting. It seems to be considered impracticable so to unite the seeds of an orange and a lemon as to blend them into one single plant from the very beginning of their growth. Undoubtedly, the operation is attended with some difficulty. Skill, and a sound knowledge of the nature and structure of seeds, are demanded of those who would perform it. For that reason, indeed, it was, that we offered a valuable reward to the first who should succeed. Had it been a mere puzzle, which could be solved by some lucky accident, we should have consigned it to the limbo of rebuses, charades, and similar puerilities. But knowledge and the power of applying it were demanded, and for this reason it appeared to be an excellent subject for,experiment; certainly not merely for the sake of a trifacial orange, which might be easily obtained in Alexandria.
We have already stated, in reply to an inquirer, that it would probably facilitate the operation if the surfaces to be united are pared down, just as is done when common grafts are united. But we are by no means sure that this is indispensable. On the contrary, many facts indicate that mere contact will produce the necessary union. No one can be ignorant that cucumbers often come as twins; so do nectarines; and we have now before us a pair of Coe's Golden Drop Plums completely united for about half their length. In all such cases, no removal of the surface of the parts took place where they joined. They united in consequence of being firmly pressed together when retry young, and in the early stage of growth, while the tissues were young, tender, and forming fast.
A similar example is presented by the monstrous apple of which a figure is annexed. In this instance, two apple flowers, accidentally brought into close contact in the earliest state of the bud, being kept firmly in contact as they advanced ingrowth, ended by becoming half incorporated; notwithstanding which, they finally became a twin fruit, consisting of two very unequal halves. In the smaller only four cells of the seed were formed; in the larger, but three. In other respects the structure was complete; but each was furnished with a pair of elevated lines on the side next the line of junction, as shown in the figure. The nature of these lines is unknown to us. What is particularly deserving of attention here is, that the hairy surface of the young apple flower offered no obstacle to the junction in question; possibly it took place before the hairs had formed.
Such being the case, it becomes a question whether, in grafting seeds, it is at all necessary that the embryos should themselves unite. It may be indeed conceived that the firm, solid, highly carbonised, and scarcely azotized tissue of which such an embryo as that of the orange consists, would, from its very nature, be unlikely to form an adhesion; just, indeed, as grafters find that old wood is very difficult to operate upon. It is by the young tisane, when first growing, soft, tender, succulent, and rich in azotiied matter, that junctions are effected. Is it not, then, highly probable, that if embryos are to be grafted on each other, the union must take place between the surfaces of the young radicle and the tender lengthening stem when first born? We think so. And upon that supposition, it may be a question whether the operation now under discussion may not be most easily and certainly performed by allowing the embryos to enter upon the early stage of germination before they are finally tied together.
Suppose 'a couple of orange pips were allowed to grow just long enough to be handled, and then had, in each case, one of the cotyledons removed, so that the nascent stems could be secured to each other with collodion, or a film of India-rubber, or some such elastic matter. We only throw this out as a suggestion.