Gardeners’ Chronicle, (926): 217-219 (Sept. 24, 1904)

GRAFT HYBRIDS
(SEE FIGS. 85 TO 88.)

FIG. 84.—FLOWERING SPRAY OF CYTISUS PURPUREUS.

YEARS ago the possibility of effecting a cross or intermixture of characters by means of grafting was not admitted by the generality of gardeners. It is true that in most instances of grafting little or no structural change is visible. The stock apparently goes on in its way, the scion follows its own course. The exceptions are so few that it has been accepted almost as a dogma that the stock does not affect the scion, nor the scion the stock. But although we are unable to see the change by our unassisted vision, it by no means follows that no change takes place. The exceptions, few though they are, are increasing in number to such an extent that it is fair to assume that changes lo take place, even though our coarser perceptions may not reveal them to us. Besides, what do we graft for if not to secure some change that is advantageous to us?

This is one of those numerous questions which cannot be settled except by prolonged experiment and observation. The most brilliant experimenter in this field of late years is Professor Daniel, of Bennes, to whose extraordinary experiments we have from time to time alluded. In the various forms of lopping, pruning, cutting back, and the like, the balance between the absorption by the roots and the food-forming work of the leaves is forcibly disturbed. A frequent consequence is the production of a number of shoots, manifesting increased vigour and often change of form. One such instance in a Pear-tree has lately been made the subject of investigation by Professor Daniel. The Pear in question had been headed back, and it produced from the stock shoots with leaves like those of the Quince, whilst three others, from the point of union of stock and scion, formed leaves intermediate in their characters between those of the Quince and those of the Pear. In this case the stock formed leaves of its kind, the scion leaves proper to a Pear, but in addition there were formed from the, point of union (bourrelet) leaves of an intermediate character, partly appertaining to the Quince, partly to the Pear. A comparative examination of the microscopical anatomy of the leaves revealed variations in minute structure analogous to those seen by the naked eye. Internal structure therefore, as well as external conformation, showed that the new shoots were examples of graft hybridisation.

*Daniel, L. "Théorie des capacités fonctionelles variations specifiques dans le greffage, Congrès do Lyon, November 1901."—Revue Générale de Botanique, t. xvi. 1904, p. 5.

The classical examples of graft hybridisation hitherto have been the Medlar of Bronvaux, and the Adam's Laburnum, to which reference has frequently been made in these columns. To these we must now add the numerous cases observed by M. Daniel.*

The history of the Adam's Laburnum, originally raised in 1826, is well known, and is cited in most of the more important text. books. Nevertheless the changes are so extraordinary that it is not wonderful that we should receive numerous specimens and enquiries about it every year.

At fig. 85 is shown a flower raceme of the ordinary Laburnum with yellow flowers; a leaf is also shown in fig. 87. Cytisus purpureus is illustrated in fig. 84, copied from the Botanical Magazine. Its habit, foliage, and lilac flowers are widely different from those of the Laburnum. Now, when the French gardener Adam budded the C. purpureus on to the Laburnum, the result was the production, after a time, of branches on the same tree, some bearing foliage and flowers of the Laburnum, others those of Cytisus purpureus, and yet others showing every intermediate stage between the two.

Our illustration at fig. 86 shows a tree of this kind, about 20 feet in height, in the nursery of Messrs. Pennick & Co., near Dublin; and by the aid of a magnifying glass these intermediate forms can be seen intermixed with the normal racemes of the Laburnum and of C. purpureus. The tree was described in our columns by Mr. Dillwyn in 1841 and 1842, and full references to this and other graft-hybrids are made in Braun's Rejuvenescence (Ray Society, 1853); Morren, Belgique Horticole, 1871; Masters in Popular Science Review, April, 1871; Sturtevant in Transactions of the Massachusetts Horticultural Society, 1881; and Darwin, Variations of Animals and Plants, ed. 2, vol. i. (1875), p. 413.

FIG. 85—FLOWERS OF COMMON LABURNUM.
FIG. 87.—TO THE LEFT, LEAF OF LABURNUM; TO THE RIGHT, LEAF OF CYTISUS PURPUREUS.

The practical side of the graft hybridisation question is one of enormous importance, especially in the Wine-growing districts. When the Phylloxera bid fair to effect the ruin of the vineyards, various methods were adopted to check or counteract the evil. The most successful means up to this point has been the grafting of the Vine on to some American stocks, the roots of which are more or less resistant to the evil influence of the Vine louse. There can be no question of the advantages that have accrued from this practice.

FIG. 86.—TREE OF CYTISUS ADAMI [GRAFT HYBRID] IN THE NURSERY OF MESSRS. PENNICK AND CO.
FIG. 88.-FLOWERING SPRAYS OF CYTISUS ADAMI (GRAFT HYBRID).

In conformity with the general opinion as to the want of influence of the stock on the scion, it has been asserted that the quality of the wine yielded by the grafted vines is not impaired, that the wine made from the grafted vines is as good in quality as that from the vines grown on their own roots.

Professor Daniel combats this view, and in a remarkable article on the "Reconstitution du Vignoble Français," in the Revue de Viticulture, shows that changes do take place as a consequence of grafting, and that if these be admitted, a great deal more investigation is required to ensure a proper selection of the stocks so as to avoid any deterioration of the Vines. We cannot enter into details the validity of which is open to discussion, but we may add that M. Daniel advocates the practice of hybridisation and selection by means of which it may be possible in the future to secure Vines on their own roots which shall be resistant to the attacks of the Phylloxera, and which shall produce the highest quality of wine without the risk of contamination consequent on grafting.

Grafting, as has been stated, disturbs the equilibrium of growth, and may therefore he injurious. The culture of the Vine on its own roots is, according to M. Daniel, the only method of conserving the normal balance of growth indispensable to the maintenance of the health of the Vine and the excellence of its produce. Resistant stocks (ungrafted) have yet to be created. Meanwhile every means must be taken to combat the Phylloxera by the use of insecticides and similar measures. Whether M. Daniel's conclusions be accepted or no, whether he and others can succeed in finding or creating a Vine so resistant to the Phylloxera that grafting will be no longer necessary, are questions which will require years of experiment for their solution. Till some definite conclusion is arrived at the French growers will probably and rightly continue to avail themselves of the American stocks.

Enough has been said to show how phenomena regarded by practical men as merely curious and not worthy their attention from an economic point of view, are in reality of the very greatest practical importance, and deserving all the study that physiologists and cultivators alike can bestow on them.

Daniel bibliography