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 (Viscum), but is not of common occurrence in other plants, even in such cases as the orange (Citrus), the Cycadeæ, Coniferæ, &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 Cratægus 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 circumstance 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.