t. i, p. 304, tab. xiii, xiv. Weber. 'Verhandl. Nat. Hist.

Vereina f. d. Preuss. Rheinl. u. Westphal.,' 1860, p. 332, tab.

vi. et vii.

=Synspermy, or Union of the Seeds.=--Seeds may be united together in various degrees, either by their integuments,[55] or by their inner parts. Such union of the seeds, however, is of rare occurrence. It takes place normally, to a slight extent, in certain cultivated forms of cotton, wherein the seeds are aggregated together into a reniform ma.s.s, whence the term kidney cotton. Union of the parts of the embryo is treated under another head (see Synophty).

=Adhesion between the axes of different plants.=--Under this head may be cla.s.sed the union that takes place between the stems, branches, or roots of different plants of the same species, and that which occurs between individuals of different species; the first is not very different in its nature from cohesion of the branches of the same plant (figs. 21, 22).

It finds its parallel, under natural circ.u.mstances, among the lower cryptogams, in which it often happens that several individual plants, originally distinct, become inseparably blended together into one ma.s.s.

In the gardening operations of inarching, and to some extent in budding, this adhesion of axis to axis occurs, the union taking place the more readily in proportion as the contact between the younger growing portions of the two axes respectively is close. The huge size of some trees has been, in some cases, attributed to the adnation of different stems. This is said to be the case with the famous plane trees of Bujukdere, near Constantinople, and in which nine trunks are more or less united together.[56]

[Ill.u.s.tration: FIG. 21.--Adhesion of two distinct stems of oak, or possibly cohesion of branches of the same tree. 'Gard. Chron.,' 1846, p.

252.]

A similar anastomosis may take place in the roots. Lindley cites a case wherein two carrots, of the white Belgian and the red Surrey varieties respectively, had grown so close to each other that each twisted half round the other, so that they ultimately became soldered together; the most singular thing with reference to this union was, that the red carrot (fig. 23, _b_), with its small overgrown part above the junction, took the colour and large dimensions of the white Belgian (_d_), which, in like manner, with its larger head above the joining (_a_), took the colour and small dimensions of the red one at and below the union (_e d_). The respective qualities of the two roots were thus transposed, while the upper portions or crowns were unaffected: the root of one, naturally weak, became distended and enlarged by the abundant matter poured into it by its new crown; and in like manner the root of the other, naturally vigorous, was starved by insufficient food derived from the new crown, and became diminutive and shrunken (see Synophty).

[Ill.u.s.tration: FIG. 22.--Adhesion of the branches of two elms. 'Gard.

Chron.,' 1849, p. 421.]

The explanation of the fact that the stumps of felled fir trees occasionally continue to grow, and to deposit fresh zones of wood over the stump, depends on similar facts. In _Abies pectinata_, says Goeppert,[57] the roots of different individuals frequently unite; hence if one be cut down, its stump may continue to live, being supplied with nourishment from the adjacent trees to which it is adherent by means of its roots.

[Ill.u.s.tration: 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 ill.u.s.trations 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 ill.u.s.tration may be cited in the fact that it has also been found possible to graft a scion on the leaf in the orange.[59]

[Ill.u.s.tration: 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 (_Visc.u.m_), 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 gra.s.ses, has been recorded[60]. Moquin-Tandon[61] relates a case wherein, by accident, a branch of a species of _Sophora_ pa.s.sed 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 cla.s.sical 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 cla.s.sical writers may be attributed to intentional or accidental fallacy, as in the so-called "greffe des charlatans" of more modern days.

Adhesion of the roots of different species has been effected artificially, as between the carrot and the beet root, while Dr. Maclean succeeded in engrafting, on a red beet, a scion of the white Silesian variety of the same species. In all these cases, even in the most successful grafts, the amount of adhesion is very slight; the union in no degree warrants the term fusion, it is little but simple contact of similar tissues, while new growing matter is formed all round the cut surfaces, so that the latter become gradually imbedded in the newly formed matter.

=Synophty or adhesion of the embryo.=--This often occurs partially in the embryo plants of the common mistleto (_Visc.u.m_), but is not of common occurrence in other plants, even in such cases as the orange (_Citrus_), the _Cycadeae_, _Coniferae_, &c., where there is frequently more than one embryo in the seed. Alphonse De Candolle has described and figured an instance of the kind in _Euphorbia helioscopia_, wherein two embryo plants were completely grafted together throughout the whole length of their axes, leaving merely the four cotyledons separate. A similar adnation has been observed by the same botanist in _Lepidium sativum_ and _Sinapis ramosa_, as well as in other plants.[64] I have met with corresponding instances in _Antirrhinum majus_ and in _Crataegus oxyacantha_, in the latter case complicated with the partial atrophy of one of the four cotyledons. It is necessary to distinguish between such cases and the fallacious appearances arising from a division of the cotyledons. M. Morren has figured and described the union of two roots of carrot (_Daucus_), which were also spirally twisted. He attributes this union to the blending of two radicles, and applies the term "rhizocollesy" to this union of the roots.[65] Mr. Thwaites cites a case wherein two embryos were contained in one seed in a _Fuchsia_, and had become adherent. What is still more remarkable, the two embryos were different, a circ.u.mstance attributable to their hybrid origin, the seed containing them being the result of the fertilisation of _Fuchsia coccinea_ (quere _F. magellanica?_) by the pollen of _F. fulgens_.

FOOTNOTES:

[30] Wydler, 'Flora,' 1852, p. 737, tab. ix.

[31] 'El. Ter. Veg.,' p. 254.

[32] 'Bull. Soc. Bot. Fr.,' 1857, p. 451.

[33] 'Bull. Acad. Belg.,' vol. xix, part ii, p. 335.

[34] 'Bull. Soc. Bot. Fr.,' 1860, p. 25.

[35] 'Bull. Soc. Bot. Fr.,' 1861, p. 147.

[36] 'Bull. Acad. Belg.,' vol. xviii, part ii, p. 498.

[37] See also Prillieux, 'Bull. Soc. Bot. Fr.,' 1861, p. 195.

[38] 'Mem. Acad. Toulouse,' 5th Series, vol. iii.

[39] Linnaea, vol. ii. p. 607.

[40] 'Journal Roy. Hort. Soc.,' new ser., vol. i. 1866, p. 200.

[41] 'Bull. Soc. Bot. Fr.,' 1861, p. 159.

[42] Ibid., 1859, p. 467.

[43] 'Flora,' 1858, p. 65, tab. ii.

[44] C. Morren. 'Bull. Acad. Belg.,' vol. xv (Fuchsia, p. 89); vol.

xviii, p. 591. (Lobelia, p. 142); vol. xix, p. 352; vol. xx, p. 4.

[45] 'Bull. Soc. Bot. Fr.,' vol. vii, p. 625.

[46] Cramer, 'Bildungsabweichungen,' p. 56, tab. vii, fig. 10, figures a case wherein the two central flowers of the capitulum of _Centaurea Jacea_ were united together.

[47] 'Bull. Bot.' tab. iii, figs. 4-6.

[48] 'Mem. greffe Ann. Science Nat.,' ser. i, t. xxiv, p. 334.

[49] "Mespilus portentosa." Poit. et Turp., 'Pomol. Franc.,' liv, x.x.xi, p. 202, pl. 202.

[50] d.u.c.h.esne, 'Hist. Nat. Frais.,' p. 79.

[51] De Cand., 'Phys. Veget.,' tom. ii, p. 781.

[52] Sched. de monstr. plant. 'Act. Helv.,' tab. i, fig. 8.

[53] 'Mem. greffe,' loc. cit., tab. xxiv, p. 334.

[54] 'Bull. Soc. Bot. Franc.,' 8, pp. 73 and 351, tab. ii; and Rose.

'Bot. Zeit.,' x, p. 410.

[55] _Nymphaea lutea_, _aesculus Hippocastanum_, &c. See Moquin, 'El.

Ter. Veg.,' p. 277.

[56] C. Martins, 'Promenade Botanique,' p. 8.