Gardeners' Chronicle, p 84 (February 5, 1898)

A "Mixed" Method of Grafting

THE relation between the stock and the scion is a subject to which reference has frequently been made in these columns. What is known as KNIGHT'S law, which VAN MONS expressed still more clearly, asserts that "only its own nature controls the development of the scion." It has, however, been proved that the statement is not universally true, and that the scion and the stock mutually influence each other more or less. Sometimes one predominates in influence, and sometimes the other; and a very important series of experiments in this connection is contained in VÖCHTING'S Ueber Transplantation am Pflanzenkörper, which was published a few years ago. Much additional and corroborative information has since been recorded by various observers, more especially perhaps by Prof. DANIEL, of the University of Bovines, in Brittany, who, in the Comptes Rendus (t. cxxv., No. 18), has lately given on the subject an elaborate account of recent experiments, which are all the more important, inasmuch as they tread on what may be called new ground in the field of the graft.

M. DANIEL mentions at the outset that in the ordinary methods of grafting, care is taken as a rule to suppress all the shoots of the stock at the time of the operation. Occasionally, and in order to facilitate the rise of the sap to the level of the graft, a bud or a few leaf-bearing shoots are retained at the apex of the stock. This procedure is, however, always of a temporary character, and the removal of all growths of this nature is effected after the graft has "taken," because, as is commonly said, the existence of the scion would be seriously compromised by the more rapid development of the stock itself. M. DANIEL asserts that no attempt had ever been made to observe the effect of leaving a certain number of shoots on the stock, and keeping their development within bounds so as to preserve the life of the scion. He commenced his experiments on the hypothesis that different results should be obtainable—as regards the success of the operation itself, and also in respect to the reciprocal reactions of the scion and stock—if it were possible to maintain an artificial equilibrium between the parts, which would then simultaneously assimilate, and elaborate sap derived from one and the same source. M. DANIEL calls his new method the "mixed graft," to distinguish it from the other ordinary systems.

He states that whilst it is an easy matter to graft successfully plants with persistent leaves on certain other plants whose leaves are non-persistent, the inverse method is difficult, if not impossible; inasmuch, as the stock, when it is deprived of its persistent leaves by the ordinary process of grafting, exists in the winter practically at the expense of the scion which, being itself leafless by nature during the same period, is unable to render the necessary help. To this cause, M. DANIEL attributes the failure of the "ordinary" method in this connection.

In the spring of 1891, M. DANIEL grafted the wild Cherry (Cerasus avium) on the Cherry-laurel (Prunus lauro-cerasus), leaving on the stock certain shoots of which the young leaves were pinched back as soon as their development assumed proportions prejudicial to the scion. In the following year, too large a number of leaves was intentionally left on the stock, with the result that the scion suffered both in its development and from insect attacks. When, however, the stock was subjected to severe pruning, the scion was restored to its normal conditions, and when in subsequent seasons, the number of leaves left on the stock was proportionate to the growth of the scion, a perfect equilibrium between the two plants was obtained, and their growth was normal. The scion, moreover, has since borne fruit on two occasions, and some of its shoots have attained a length exceeding 1 yard annually. M. DANIEL therefore considers this union to have been completely successful, and he is of opinion, at any rate in the case of the two plants above-mentioned, that the "mixed method" offers a better means of grafting a tree with non-persistent leaves on an evergreen.

Another series of experiments was undertaken by grafting two different kinds of Haricot Beans. The grafting of Haricot Beans, as well as of other hollow-stemmed plants, had apparently been considered impracticable until M. DANIEL at the "French Association" meeting in 1892 announced its possibility by grafting the plants during the period of germination. In order the better to observe the differences between the "ordinary "and "mixed" methods in this connection, M. DANIEL selected two varieties with maximum characteristic differences, viz., the Black Belgian and the Soissons Haricots. The former is a dwarf and somewhat early plant, with a short inflorescence, bearing from three to five violet flowers, yielding two or three pods, which are tender and agreeable to the taste, and bearing dark-violet, medium-sized seeds. The Soissons Bean, on the other hand, is a Runner Bean, and a much later plant; its long inflorescence bears about twenty pale yellow flowers, with three to five coarse pods of a disagreeable taste, and its seeds are white and large.

Mr. DANIEL experimented with plants growing side by side under exactly similar conditions, in order to obtain comparative results of the two different methods of grafting, and he also grew plants of each variety under normal conditions, so as to serve as checks on the variations obtained. The results are shown in the following tabular statement:—

  Soissons Haricot Black Belgian Haricot on Soissons Haricot Black Belgian Haricot
Not Grafted 'Mixed Grafts" "Ordinary Graft" Not Grafted
Height   4.50 metres 0.40 metres 0.25 metres 0.40 metres
Leaves Very numerous; very large. Very numerous; very large Less numerous, paler green, and less vigorous Numerous and vigorous.
Flowers Pale Yellow Some violet, others variegated white and violet. Violet (all) Violet (all)
Flower-stalks Long: about twenty flowers; three to five pods. One long stalk, bearing nine variegated flowers. The others short, similar to the "check" plant. The long one bore three pods. Short; two or three flowers, one or two pods. Short; three to five flowers, two or three pods.
Pods Stringy; taste peculiar, and very disagreeable Partly stringy, with pronounced taste of Soissons Bean Slightly stringy; slightly like Soissons Bean in taste. Tender, not stringy; taste very agreeable.
Seeds White Dark violet Dark violet Dark violet.

The conclusions drawn by M. DANIEL from these experiments are as follows:—

The "mixed method" of grafting should be adopted to ensure more easily the union between plants of marked physiological differences, as in the case of persistent and deciduous leaves.

The direct influence of the stock on the scion is not identical in the "mixed" and in the "ordinary" methods. Those phenomena which may be considered due to variations in the surrounding conditions, as are the size and relative vigour of the scion, are less marked in the case of the "mixed" method. On the contrary, certain characteristics of the stock, such as its taste, the shape of its fruit, and the colour of its flowers, are much more easily conveyed to the scion by the "mixed" method, which should be used when it is desired to obtain by means of the graft new varieties possessing certain particular characteristics; or, in other words, to make the scion or its posterity acquire certain qualities of a given stock. Conversely, when the aim is to maintain the purity of the variety to which the scion belongs, the "ordinary" methods should be adopted, leaving, moreover, on the stock the smallest possible proportion of green parts—that is to say, to operate as near the root as is possible.

Daniel bibliography