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Show 264 CAUSES OF VARIABILITY. CHAP. xxrr. the womb.32 This view is evidently not applicable to the lower animals, which lay unimpregnated eggs, or to plants. D1~. William Hunter, in the last century, told my father that durmg many years every woman in a large London Lyin~-in Hospital. was asked before her confinement whether anythmg had specially affected her mind, and the answer was written clown ; and it so happened that in no one instance could a coincidence be detected between the woman's answer and any abnormal structure; but when she knew the nature of the structure, she frequently suggested some fresh cause. The belief in the power of the mother's imagination may perhaps have arisen from the children of a second marriage resembling the previous father, as certainly sometimes occurs, in accordance with the facts given in the eleventh chapter. Grossing as a Gause of Variability.-In an early part of this chapter it was stated that Pallas 33 and a few other naturalists maintain that variability is wholly due to crossing. If this means that new characters never spontaneously appear in our domestic races, but that they are all directly derived from certain aboriginal species, the doctrine is little less than absurd; for it implies that animals like Italian greyhounds, pug-dogs, bull-dogs, pouter and fantail pigeons, &c., were able to exist in a state of nature. Hut the doctrine may mean something widely different, namely, that the crossing of distinct species is the sole cause of the first appearance of new characters, and that without this aid man could not have formed his various breeds. 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, almost certain that the breeds of various animals, such as of the rabbit, pigeon, duck, &c., and the varieties of several plants, are the modified descendants of a single wild species. N evertheless, it is probable that the crossing of two forms, when one or both have long been domesticated or cultivatcJ, adds to the variability of the offspring, independently of the commingling of the characters derived from the two parent-forms; and this implies 32 Muller has conclusively argued against this belief, 'Elements of Phys.,' Eng. trauslat., vol. ii., 1842, p. 1405. 33 'Act. Acad. St. Petersburg,' 1780, part ii. p. R4, &c. CHAP. XXII. CAUSES OF VARIABILITY. 265 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 dis6nguish between the reappearance of ancient characters and the first appearance of new characters. Practically, whether new or old, they would be new to the breed in which they reappeared. Gartner declares,34 and his experience is of the highest value on such a point, that, when he crossed native plants which had not been cultivated, be 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 band, 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.35 Prof. Lecoq 36 speaks strongly to the Rame effect in regard to this same genus, and asserts that many of the hybrids from Mirabilis j-dapa 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. i ulapa. Herbert, also, bas described 37 the offspring from a hybrid Rhododendron as being " as unlilce all others in foliage, as if they bad been a "separate speeies." The common experience offloriculturists proves that the crossing and recrossing of distinct but allied plants, such as the species of Petunia, Calceolaria, Fuchsia, Verbena, &c., induces excessive variability; hence the appearance of quite new characters is probable. M. Carriere 38 has lately discussed this subject: be states that Erythrina cristayalli bad 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 34 'Bastarderzeuguug,' s. 249, 255, 295. 35 'Nova Acta, St. Petersburg,' 1794-, p. 378; 1795, pp. 307, 313, 316; 1787, p. 407. 36 'De la Fecondation,' 1862, p. 311. 3i 'Amaryllidacere,' 1837, p. 362. 38 Abstracted in 'Gard. Chronicle, 1860, P·. 1081. |