Fig. 23.—Adhesion of two roots of carrot. 'Gard. Chron.,' 1851, p. 67.
A not uncommon malformation in mushrooms arises from the confluence of their stalks (fig. 24), and when the union takes place by means of the pilei, it sometimes happens, during growth, that the one fungus is detached from its attachment to the ground, and is borne up with the other, sometimes, even, being found in an inverted position on the top of its fellow.[58]
The garden operations of budding, grafting and inarching have already been alluded to as furnishing illustrations of adhesion, but it may be well to refer briefly to certain other interesting examples of adhesion induced artificially; thus, the employment of the root as a stock, "root-grafting," is now largely practised with some plants, as affording a quicker means of propagation than by cuttings; and a still more curious illustration may be cited in the fact that it has also been found possible to graft a scion on the leaf in the orange.[59]
Fig. 24.—Section through two adherent mushrooms, the upper one inverted.
Mr. Darwin, in his work on the 'Variation of Animals and Plants,' vol. i, p. 395, alludes to the two following remarkable cases of fusion:—"The author of 'Des Jacinthes' (Amsterdam, 1768, p. 124) says that bulbs of blue and red hyacinths may be cut in two, and that they will grow together, and throw up a united stem (and this Mr. Darwin has himself seen), with flowers of the two colours on the opposite sides. But the remarkable point is, that flowers are sometimes produced with the two colours blended together." In the second case related by Mr. Trail, about sixty blue and white potatoes were cut in halves through the eyes or buds, and the halves were then joined, the other buds being destroyed. Union took place, and some of the united tubers produced white, others blue, while some produced tubers partly white and partly blue.
Adhesion of the axes of plants belonging to different species is a more singular occurrence than the former, and is of some interest as connected with the operation of grafting. As a general rule horticulturists are of opinion, and their opinion is borne out by facts, that the operation of grafting, to be successful, must be practised on plants of close botanical affinity. On the other hand, it is equally true that some plants very closely allied cannot be propagated in this manner. Contact between the younger growing tissues is essential to successful grafting as practised by the gardener, and is probably quite as necessary in those cases where the process takes place naturally. Although there is little doubt but that some of the recorded instances of natural or artificial grafting of plants of distant botanical affinities are untrustworthy, yet the instances of adhesion between widely different plants are too numerous and too well attested to allow of doubt. Moreover, when parasitical plants are considered, such as the Orobanches, the Cuscutas, and specially the mistleto (Viscum), which may be found growing on plants of very varied botanical relationship, the occurrence of occasional adhesion between plants of distant affinity is not so much to be wondered at. Union between the haulms of wheat and rye, and other grasses, has been recorded[60]. Moquin-Tandon[61] relates a case wherein, by accident, a branch of a species of Sophora passed through the fork, made by two diverging branches of an elder (Sambucus), growing in the Jardin des Plantes of Toulouse. The branch of the Sophora contracted a firm adhesion to the elder, and what is remarkable is that, although the latter has much softer wood than the former, yet the branch of the harder wooded tree was flattened, as if subjected to great pressure[62]. It is possible that some of the cases similar to those spoken of by Columella, Virgil[63], and other classical writers, may have originated in the accidental admission of seeds into the crevices of trees; in time the seeds grew, and as they did so, the young plants contracted an adhesion to the supporting tree. Some of the instances recorded by classical writers may be attributed to intentional or accidental fallacy, as in the so-called "greffe des charlatans" of more modern days.