Page:Darwinism by Alfred Wallace 1889.djvu/102

80 subsequently shows that, in Xanthoxylum monogynum, 'it often happens that on the same plant, on the same panicle, we find flowers with one or with two ovaries;' and that this is an important character is shown by the Rutaceæ (to which Xanthoxylum belongs), being placed in a group of natural orders characterised by having a solitary ovary."

"De Candolle has divided the Cruciferæ into five sub-orders in accordance with the position of the radicle and cotyledons, yet Mons. T. Gay (Ann. des Scien. Nat., ser. i. tom. vii. p. 389) found in sixteen seeds of Petrocallis Pyrenaica the form of the embryo so uncertain that he could not tell whether it ought to be placed in the sub-orders 'Pleurorhizée' or 'Notorhizée'; so again (p. 400) in Cochlearia saxatilis M. Gay examined twenty-nine embryos, and of these sixteen were vigorously 'pleurorhizées,' nine had characters intermediate between pleuro- and notor- hizées, and four were pure notorhizées."

"M. Raspail asserts (Ann. des Scien. Nat., ser. i. tom. v. p. 440) that a grass (Nostus Borbonicus) is so eminently variable in its floral organisation, that the varieties might serve to make a family with sufficiently numerous genera and tribes—a remark which shows that important organs must be here variable."

The preceding statements, as to the great amount of variation occurring in animals and plants, do not prove that all species vary to the same extent, or even vary at all, but, merely, that a considerable number of species in every class, order, and family do so vary. It will have been observed that the examples of great variability have all been taken from common species, or species which have a wide range and are abundant in individuals. Now Mr. Darwin concludes, from an elaborate examination of the floras and faunas of several distinct regions, that common, wide ranging species, as a rule, vary most, while those that are confined to special districts and are therefore comparatively limited in number of individuals vary least. By a similar comparison it is shown that species of large genera vary more than species of small genera. These facts explain, to some extent, why the opinion has been so prevalent that variation is very limited in amount and exceptional in character. For