OCR Text |
Show g~ VARIETIES IN PJ.ANTS [Ch. II. d . t tl ommon wheat and that some animal of transforme HI o 1e c ' the O'enus cam·s , s t'll unreclaimed has been metamot·phosed 1 ' • . 0 wto the d og, mere 1y because we cannot find the domestic dog, or t 11 e cu 1t i·v a t ed wheat ' in a state of nature, we may be next ca1 1 ed upon t oma'l"·e similar admissions in regard to. the ca.m el; for 1· t seems ve1. y doubtful whether any race of this spectes of quadruped is now wild. . . But if agr'iculture, it will be said, does no_t su~ply exampl~s of extraordinary changes of form and orgamzatron, the horli- cu 1t un·s t can, at least ' appeal to facts which may confound the preceding train of reasoning. The crab has been trans. formed into the apple; the sloe into the plum : flowers have chanO'ed their colour and become double; and these new characte~ s can be perpetuated by seed,-a bitter plant with wavy sea-O'reen leaves has been taken from the sea-side where it grew like :ild charlock, has been transplanted into the gar?en, lost its saltness, and has been metamorphosed into two distinct vegetables as unlike each other as is each to the parent plant-the red cabbage and the cauliflower. These, and a multitude of analogous facts, are undoubtedly among the wonders of nature, and attest more strongly, perhaps, the extent to which species may be modified, than any examples derived from the animal kingdom. But in these cases we find, that we soon rea~h ~e~tain limits, beyond which we are unable to cause the mdivlduals, descending from the same stock, to vary; while, on the other hand, it is easy to show that these extraordinary varieties could seldom arise, and could never be perpetuated in a wild state for many generations, under any imaginable combination of accidents. They may be regarded as extreme cases brought about by human interference, and not as phenomena which indicate a capability of indefinite modification in the natural world. The propagation of a plant by buds or grafts, and by cuttings, is obviously a mode which nature does not employ; and this multiplication, as well as that produced by roots and layers, seems merely to operate as an extension of the life of an indivi· Ch. II.] PRODUCED BY HORTICULTURE, 33 dual, and not as a reproduction of the species, as happens by seed. All plants increased by the former means retain precisely the peculiar qualities of the individual to which they .owe their origin, and, like an individual, they have only a detel'minate existence ; in some cases longer and in others shorter*. It seems now admitted by horticulturists, that none of our garden Yarieties of fruit are entitled to be considered strictly permanent, but that they wear out after a time i"; and we are thus compelled to resort again to seeds; in which case, there is so decided a tendency in the seedlings to revert to the original type, that our utmost skill is sometimes baffled in attempting to recover the desired variety. 'l'he different races of cabbages afford, as we have admitted, an astonishing example of deviation from a common type ; but we can scarcely conceive them to have originated, much less to have lasted for several generations, without the intervention of man. It is only by strong manures that these varieties have been obtained, and in poorer soils they instantly degenerate. If, therefore, we suppose in a state of nature the seed of the wild Brassica oleracea to have been wafted from the sea-side to some spot enriched by the dung of animals, and to have there become a cauliflower, it would soon diffuse its seed to some comparatively steril soils around, and the offspring would relapse to the likeness of the parent stock, like some individuals which 'may now be seen growing on the cornice of old London bridge. But if we go so far as to imagine the soil, in the spot first occupied, to be constantly manured by herds of wild animals, so as to continue as rich as that of a garden, still the variety could not be maintained, because we know that each of these races is prone to fecundate others, and gardeners are compelled to exert the utmost diligence to prevent cross-breeds. The intermixture of the pollen of varieties growing in the poorer soil around, would soon destroy the peculiar characters ,.,. Smith's Introduction to Botany, p. 138. Edit. 1807. f See Mr. Knight's Observations, Hort. Trans., vol. ii., p. 160. Vor .. II. D |