Gardeners’ Chronicle, 42(1094): 414 (December 14, 1907)
The Mutual Relations of Graft and Scion

A considerable amount of doubt attaches to many of the statements, sometimes rather confidently put forward, as to the nature of the influence mutually exerted on each other by scion and stock in grafts. Nobody, of course, will refuse to admit that some sort of influence on the scion is likely to occur, since the condition of water supply is largely affected by the rooting character of the stock. But this is not the same thing as saying that a definite substance can pass from one to the other and produce specific differences of a material kind in the two consorting parts of the plant. There are instances, however, in which there seems to be good reason for thinking that such a transmission may occur. When variegated sports are grafted on to the normal green stock, it may happen that shoots which spring from the latter at a point below the insertion of the scion exhibit the phenomenon of variegation. In such a case it is difficult to resist the inference that some substance, probably some chemical substance, has passed from the scion to the lower part of the plant, and has there given rise to the same peculiarity which it had excited in the introduced shoot. It is certain that the substances common to both parts of the plant can travel from one to the other, for the sugars, &c., which are manufactured in the leaves must pass down to nourish the roots of the stock. But it is not so clear whether other substances can so pass, and yet definite information on this point is very desirable in order to enable us to give a rational explanation as to how the two parts of a grafted plant may influence each other, and to what extent interchange of substances peculiar to each is possible.

*Sur la variation de la quantité d'atropine ... dans les greffes de Belladone et de Tomate. Travaux scientifiques de l'Université de Renne,. Tome V.

Some recent experiments and observations of M. Ch. Laurent* have an interesting bearing on these questions, and are worth the attention of those who are interested in the theory and practice of grafting. It is a matter of no great difficulty to graft the deadly Nightshade (Atropa Belladonna) upon the Tomato. Both are, of course, Solanaceous plants, but the former is well characterised by its poisonous properties, which it owes to the presence of the alkaloid atropin. The object of the experiments was to ascertain whether the alkaloid would pass into the Tomato, and if so to what extent. The results were of considerable interest, and may be briefly summarised here.

When the Belladonna was used as the stock, none of the poison passed into the Tomato, which produced leaves, flowers, and fruit in the ordinary way, although one might have anticipated that the atropin would have passed upwards from the rootstock. On the contrary, when the Tomato was used as the stock, the Nightshade not only produced the atropin in its own tissues but the alkaloid passed down and was recognisable in both the stem and root of the Tomato. A case of special interest was that in which the Tomato was allowed to retain some of its own branches in addition to the graft. Under these circumstances it was found that the alkaloid only permeated the tissues of the Tomato up to the level of the spot where the scion was borne, and, as might have been expected, it was more abundant in the roots and stems than in the leaves.

Now, whilst it is obviously premature to base large conclusions on the comparatively few exact investigations which have been as yet carried out in this difficult but important field of investigation, they do throw a suggestive light on the probable nature of the influence which is seen in vines, for example, when one sort has been worked on another, influences which several of our correspondents have recently pointed out in these columns, whilst indications are also afforded as to ways of possibly obviating the attacks of certain diseases.