CHAPTER III.[ToC]
The Law of Variation.
We come now to consider another law, by which that of similarity is greatly modified, to wit, the law of variation or divergence. All organic beings, whether plants or animals, possess a certain flexibility or pliancy of organization, rendering them capable of change to a greater or less extent. When in a state of nature variations are comparatively slow and infrequent, but when in a state of domestication they occur much oftener and to a much greater extent. The greater variability in the latter case is doubtless owing, in some measure, to our domestic productions being reared under conditions of life not so uniform, and different from, those to which the parent species was exposed in a state of nature.
Flexibility of organization in connexion with climate, is seen in a remarkable degree in Indian corn. The small Canada variety, growing only three feet high and ripening in seventy to ninety days when carried southward, gradually enlarges in the whole plant until it may be grown twelve feet high and upwards, and requires one hundred and fifty days to ripen its seed. A southern variety brought northward, gradually dwindles in size and ripens earlier until it reaches a type specially fitted to its latitude.
Variation, although the same in kind, is greater in degree, among domesticated plants than among animals. From the single wild variety of the potato as first discovered and taken to Europe, have sprung innumerable sorts. Kemp, in his work on Agricultural Physiology, tells us, that on the maritime cliffs of England, there exists a little plant with a fusiform root, smooth glaucous leaves, flowers similar to wild mustard and of a saline taste. It is called by botanists, Brassica oleracea. By cultivation there have been obtained from this insignificant and apparently useless plant—
1st, all borecoles or kails, 12 varieties or more.
2d, all cabbages having heart.
3d, the various kinds of Savoy cabbages.
4th, Brussels sprouts.
5th, all the broccolis and cauliflowers which do not heart.
6th, the rape plant.
7th, the ruta baga or Swedish turnip.
8th, yellow and white turnips.
9th, hybrid turnips.
10th, kohl rabbi.
Similar examples are numerous among our common useful plants, and among flowers the dahlia and verbena furnish an illustration of countless varieties, embracing numberless hues and combinations of color, from purest white through nearly all the tints of the rainbow to almost black, of divers hights too, and habits of growth, springing up under the hand of cultivation in a few years from plants which at first yielded only a comparatively unattractive and self-colored flower. In brief, it may be said, that nearly or quite all the choicest productions both of our kitchen and flower gardens are due to variations induced by cultivation in a course of years from plants which in their natural condition would scarcely attract a passing glance.