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Show 80 DARWIN!. .M: CHAP. subsequently bows that, in Xanthoxylum monogynnm,. ' it often huppcns th:-~t on the se:~mc plant, o~ t~e same pan~cl~, we find fiowers w1th one or w1th two ovanes; and that th1s 1s an important character is shown by the Rutacero (to which Xanthoxylum ~elongs), bei~g plac~d in a gro~p of natural orders characterised by havmg a sohtary ovary. "De Candollc hc.ts divided the Cruciferro into five sub-orders in accordance with the position of the radicle :tncl cotyledons, yet Mons. T. G..ty (Ann. rles Scien. Nat., sol'. i. tom. vii. p. 3 ' 9) found in sixteen seeds of Petrocalli~ Pyrcrmic<t the form of the embryo so uncertain that he could not tell whether it ought to be placed in the sub-orders 'Pleurorhizee' or 'Notorhi~:6c '; so again (p. 400) in Cochlcaria saxa~ilis M. Gay ~xa.min ccl twenty-nine embryos, and of these siXteen were v1goronsly 'pleurorhizecs,' nine had characters intermediate between plcuro- and notor- hizees, and four w~re pure noto~hizecs. " "M. Raspail asserts (Ann. des ScMn. Nld., ser. 1. tom. v. p. 440) that a grass (Nostus Borbonicus) is so eminently variable in its floral organisation, that the varieties might sc:vc to make a family with sufficiently numerous genera and trJbesa remark which shows that important organs must be here variable." Species which vary little. The preceding statements, as to the great amount of variation occurring in animals and plants, do not prov that all species vary to tho same extent, or even vary a L 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 whi ch h:tvn a wide range and are abundant in individuals. Now Mr. Darwin concludes, from an elaborate examination of the fl oras and faunas of several distinct regions, that common, wide ranging species, as a rule, vary most, while those that are confined to special diRtricts and arc therefore comparn,ti vcly limited in number of individuals vary least. By a similar comparison it is shown tha.t specie. of largo genera vary more than species of small genera. The.·c facts explain, to some extent, why the opinion has l>cen so prevalent that variation is very limited in amount and exceptional in character. For 11r VARIABILITY OF SPEOH .. S IN A STATE OF NATURE naturali. ts of the old school, and e:tll more collectors, were interested in species in proportion to their rarity, and woulu often have in their collections a larger number of specimeus of a rare species than of a species that was very common. Now as the. e rare species do really vary much le s than t 1e common specie , and in many ca es hardly vary at all, it was very natural that a belief in the fixity of species should prevail. It is not, however, as we shall see presently, the rare, but the common and widespread species which become the parents of new forms, and thus the non-varin.bility of any number of rare or local species offers no difficulty whatever in tho way of tho theory of evolution. Concluding llernarks. We have now shown in some detail, at the risk of bcin otcdious, that in<lividu:tl variability is a general character of all common all(l widespread species of animals or plants; and, further, that this variability extend , so far as we l<now, to every p:trt and organ, whether external or internal, a well ns to every mental faculty. Y ct more important i th f:tct that each part or organ varies to a considerable extent independently of other pc.trts. Again, we htwc shown, by ahnndn.nt evidence, that tho variation that occm is very hrge in amount- usually reaching 10 or 20, and sometimes even 25 per cent of tho average size of the varying part; while not one or two only, but from 5 to 10 per cent of the . pecimens examined exhibit nearly as large an }tmount of variation. These facts have been brought clearly before the reader by means of numerous diagrams, drawn to scale and exhihitinrr the actual variations in inches, so that there can be no possibility of denying either their generality or their amount .. The importance of this full exposition of the subject will he seen in future chapters, when we shall frequently have to refer to tho facts here set forth, especially when we deal with the various theories of recent· writers and the criticisms that have been made of the Darwinian theory. A full exposition of the facts of variation among wild animals and plants is the more necessary, becau e comparatively few of them were publi heel in Mr. Darwin's works, while the more important hav only been made known since G |