As, however, new characters have appeared in certain cases by bud- variation, we may conclude with certainty that crossing is not necessary for variability. It is, moreover, certain that the breeds of various animals, such as of the rabbit, pigeon, duck, etc., and the varieties of several plants, are the modified descendants of a single wild species. Nevertheless, it is probable that the crossing of two forms, when one or both have long been domesticated or cultivated, adds to the variability of the offspring, independently of the commingling of the characters derived from the two parent-forms; and this implies that new characters actually arise. But we must not forget the facts advanced in the thirteenth chapter, which clearly prove that the act of crossing often leads to the reappearance or reversion of long- lost characters; and in most cases it would be impossible to distinguish between the reappearance of ancient characters and the first appearance of absolutely new characters. Practically, whether new or old, they would be new to the breed in which they reappeared.
[Gartner declares (22/34. 'Bastarderzeugung' s. 249, 255, 295.), and his experience is of the highest value on such a point, that, when he crossed native plants which had not been cultivated, he never once saw in the offspring any new character; but that from the odd manner in which the characters derived from the parents were combined, they sometimes appeared as if new. When, on the other hand, he crossed cultivated plants, he admits that new characters occasionally appeared, but he is strongly inclined to attribute their appearance to ordinary variability, not in any way to the cross. An opposite conclusion, however, appears to me the more probable. According to Kolreuter, hybrids in the genus Mirabilis vary almost infinitely, and he describes new and singular characters in the form of the seeds, in the colour of the anthers, in the cotyledons being of immense size, in new and highly peculiar odours, in the flowers expanding early in the season, and in their closing at night. With respect to one lot of these hybrids, he remarks that they presented characters exactly the reverse of what might have been expected from their parentage. (22/35. 'Nova Acta, St. Petersburg' 1794 page 378; 1795 pages 307, 313, 316; 1787 page 407.)
Prof. Lecoq (22/36. 'De la Fecondation' 1862 page 311.) speaks strongly to the same effect in regard to this same genus, and asserts that many of the hybrids from Mirabilis jalapa and multiflora might easily be mistaken for distinct species, and adds that they differed in a greater degree than the other species of the genus, from M. jalapa. Herbert, also, has described (22/37. 'Amaryllidaceae' 1837 page 362.) certain hybrid Rhododendrons as being "as UNLIKE ALL OTHERS in foliage, as if they had been a separate species." The common experience of floriculturists proves that the crossing and recrossing of distinct but allied plants, such as the species of Petunia, Calceolaria, Fuchsia, Verbena, etc., induces excessive variability; hence the appearance of quite new characters is probable. M. Carriere (22/38. Abstracted in 'Gardener's Chronicle' 1860 page 1081.) has lately discussed this subject: he states that Erythrina cristagalli had been multiplied by seed for many years, but had not yielded any varieties: it was then crossed with the allied E. herbacea, and "the resistance was now overcome, and varieties were produced with flowers of extremely different size, form, and colour."
From the general and apparently well-founded belief that the crossing of distinct species, besides commingling their characters, adds greatly to their variability, it has probably arisen that some botanists have gone so far as to maintain (22/39. This was the opinion of the elder De Candolle, as quoted in 'Dic. Class. d'Hist. Nat.' tome 8 page 405. Puvis in his work 'De la Degeneration' 1837 page 37, has discussed this same point.) that, when a genus includes only a single species, this when cultivated never varies.