Gardeners’ Chronicle, 3. ser., (674): 398 (November 23, 1899)

The Grafting of Monocotyledons

AT various intervals during the put four or five years report. have been published in these columns relating to a series of most interesting experiments conducted by M. LUCIEN DANIEL, who, with other workers on this subject, has shown that the old theories of the science of grafting contained many fallacies. On this occasion a short reference will be made to the successful graft of monocotyledonous plants; an operation which has hitherto been supposed to be an impossibility.

It is well known that in order to ensure the union of the scion and the stock, it is necessary that the living tissue of both parts should be intimately connected. By this means the nutrition of the grafted plant becomes possible through the process of osmosis, and perhaps by continuity of the protoplasm; and the stock which extracts nourishment from the soil through its root, passes it on to the scion. The reproduction of living cells, whereby the intimate union is effected, takes place in the cambium, and in the medullary rays, which, in certain cases, play a secondary part in this connection. The graft of dicotyledonous plants is, consequently, a comparatively easy matter, because their cambium layer is continuous and well defined, in contradistinction to monocotyledons, where the generative zone lies isolated in each fibro-vascular bundle. It is indeed owing to this peculiar anatomical structure, which affords only a slender chance for the agglutination of the dissected parts, that the union of monocotyledonous plants has hitherto been considered impossible.

*Comptes Rendus, vol. cxxix., p. 654.

The experiment now under consideration is the outcome of laborious and thoughtful work, extending over many years, but which has yielded definite result, during the past summer. In the complete report which has recently been presented to the French Académie des Sciences,* M. DANIEL states that the graft of the class of plants in question was attempted at a very early period, and he refers to a system adopted by the ancient Greek gardeners, who appear to have considered that they had solved the problem. This method of THEOPHRASTUS was, however, what, in common parlance, would be called a "fraud," inasmuch as it bore no relation whatever to the graft, but consisted merely in placing seed, such as Wheat, within a tuber or root Germination took place naturally, if there was a sufficient amount of moisture; but there was never a trace of physiological union between the plants. Reference is also made to somewhat vague results reported by YSABEAU as regards grafting the Rice plant in Italy; and to DE CANDOLLE, who, in his Physiologie Végétale, published in 1832, gives an account of experiments made with a species of Dracaena, which, however, gave no satisfactory results. If, therefore, the labours of M. DANIEL have not been made on virgin soil, he claims that no previous worker in this special field of enquiry has even raised a crop, although he would be the last person to infer that his researches do more than indicate a bountiful harvest.

During the last few year. M. DANIEL has on various occasions obtained complete union of the two lips of a comparatively deep, longitudinal incision in the stem of the Lily, Iris, Canna, Funkia cordata, in the pseudo-bulb of Orchids of the genus Laelia, and even in the very young stem of a Cryptogam—Selaginella arborea. The healing of the wound in these cases led M. DANIEL to attempt the cleft-grafting of various monocotyledonous plants; but in spite of a clear, though limited, reunion of the parts, the plants did not live beyond a period of six weeks. The system of inarching, or grafting by approach, was also tried, with somewhat more satisfactory—but still unsuccessful—results in the case of different varieties of Caladium. He therefore came to the conclusion that neither of the above-mentioned methods of grafting was likely to succeed, on account of the insufficient means of communication of the asp between the stock and scion. In order, therefore, to increase the surface in contact, he tried the splice-graft, and cut the stem as obliquely as possible, and very nearly at its apex, where the scion from the same plant was replaced and ligatured very firmly. The experiment was tried, firstly, with a Vanilla, which is a small genus of climbing Orchids belonging to the order Arethuseae, and the only one which possesses any economic value, the fruit of several species producing the "vanilla" which is largely employed to flavour confectionery. In the second instance, a Philodendron was selected, a genus of tropical American plants of the family Araceae, which attach themselves to the trunks of trees, and hence their name.

The operation was made during the month of May last, and the union of the graft in question is now quite complete, and not only have the internodes of the scion elongated, but new leaves have appeared, and in one case, aerial roots have been developed. The presence of these roots is interesting, and they are regarded as a confirmatory proof of success, inasmuch as the Philodendron bears two kinds of roots, viz: those which extract nourishment from the soil, and other, which draw moisture from the atmosphere.

*Gardeners’ Chronicle, 1898, L, p. 84.

The graft in question, where the cut portion of the plant was replaced in situ, is a true graft since there has been complete re-union of the parts, and subsequent movement of sap therein, and M. DANIEL classifies it as a variety of the "mixed graft," which is the term applied to the system whereby curious physiological results are obtained when some of the leaves are allowed to remain on the scion and on the stock. This method has already been fully explained in this journal;* but in connection with monocotyledonous plants, which include so many flowers, it will be of interest to repeat in general terms that those phenomena which may be considered to be due to variation in the surrounding conditions, such as size and vigour of the plant, are less marked by the "mixed graft," which however should be employed when it is desired to obtain new varieties possessing certain characteristics, such as the shape of the fruit and the colour of the flowers.

M. DANIEL, therefore, concludes that the results obtained with Vanilla and Philodendron are an indication that the graft of monocotyledonous plants can no longer be considered impracticable, and that its success merely depends on the extent of the surfaces in contact, on the system of grafting which is employed, and on the nature of the plants.

We shall probably shortly refer at greater length to M. DANIEL'S interesting experiments.

Daniel bibliography