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Show [Ch.IV. • RARITY OF HYBRIDS AMONG 56 . . th least degree l· nrt er•w r' they cannot hardiness of hybrids be m e . even if they were . . f, ny creneratwns, maintain tbetr footmg or rna b • • wild state. In the d eneratwn m a ever produced beyon one g 1 . ht of the strongest 1 f, • existence, t le ng universal strugg c or ' 1 d durability of a race 'l d the ~trengt 1 an eventually prevm s; an ~. in which hybrids are depends mam. 1 y on 1· ts prolificness, acknowledged to be deficient. h' h evet· bears seed, and is 1 'd plant w 1c n Centaurea hy m. a, a f t intermixture of two l ·ed by the requen . supposed to be proc uc . w. wild upon a hill neaJ · f Centaurea, gro :s well-known species 0 1 steril has been produced l lacerus' a so ' Turin. Rantmcu us d ear Paris, by the union of two accidentally at Grenoble, an ~ d * r but this occurred m gar ens . Ranuncu 1; . f h' . enious papers on mule plants, M H ·bert m one o IS mg f r. ei ' ~ . their non-occurrence in a state o d rs to account !OI . • 1 en eavou . that all the combmatwns t 1at . f. the circumstance . natme, 10m h 1 ady been made many centunes were likely to occur, ave a re . . . b .· 1! d the various species of botamsts' ut m aero and have Iorme . . d . f 0 .' ·dens he says wh ene ver species ' bavmg a certam eg1ee. o our gar ' 1 ' . t ansported from different countnes, ffi 't to each ot ler, are r . . a :~b~oucrht for the first time into contact' they give nse to an b . d oecies t. But we have no data, as yet, to warrant the by rl .sp . crl permanent hybrid race has ever been concluswn, that a smo e ll' d formed, even m. gai· de"n s, b y the intermarriaoa e . of two a te f . b. 1 t from distant habitations. U ntll some fact o species roug 1 · bl f tl . kind is fairly established, and a new species, capa e o us . . If 'n a state of perfect independence of man, Perpetuatmg 1tse 1 . · . d t think it reasonable to call m questiOn can be pomte ou ' we · 'l'h ieties entirely this hypothetical source of new specie~. at va; do sometimes spring up from cross breeds, ~n a natura way, 1 dl be doubted but they probably die out even more can 1ar Y ' ra idl than races propagated by grafts or layers. . . PD y d lle whose opinion on ·a philosophical questiOn of this ecan o , d · h' Essay kind deserves the greatest attention, has observe ' m IS "' Hon. and Rev. w. Hel·bert, Hort. Trans., vol. iv., P· 41. t lbi4. Ch. IV.] PLANTS IN A WILD STATE. 57 on Botanical Geography, that the varieties of plants range themselves under two general heads: those produced by external circumstances, and those formed by hybridity. After adducing various arguments to show that neither of these causes can explain the permanent diversity of plants indigenous in different regions, he says, in regard to the crossing of races, " I can perfectly comprehend, without altogether sharing the opinion, that where many species of the same genera occur near together, hybrid species may be formed, and I am aware that the great number of species of certain genera which are found in particular regions, may be explained in this manner; but I am unable to conceive how any one can regard the same explanation as applicable to species which live naturally at great distances. If the three larches, for example, now known in the world, lived in the same localities, I might then believe that one of them was the produce of the crossing of the two others; but I never could admit that the Siberian species has been produced by the crossing of those of Europe and America. I see, then, that there exist, in organized beings, permanent differences which cannot be referred to any one of the actual causes of ;variation, and these differences are what constitute species •'/.'." The most decisive arguments, perhaps, amongst mm1y others, against the probability of the derivation of permanent species from cross breeds, are to be drawn from the fact alluded to by Decandolle, of species having a close affinity to each other occurring in distinct botanical provinces, or countries inhabited by groups of distinct species of indigenous plants. For in this case naturalists, who are not prepared to go the whole length of the transmutationists, are under the necessity of admitting, that in some cases species which approach very near to each other in their characters, were so created from their origin ; an admission fatal to the idea of its being a general law of nature, that a few original types only should be formed, * Essai El6mentaire1 &c. 3me. l>artie. |
