If now we turn to another set of plants, the turnips, radishes, carrots, and potatoes, we find that the roots or underground tubers have been wonderfully enlarged and improved, and also altered in shape and colour, while the stems, leaves, flowers, and fruits have remained almost unchanged. In the various kinds of peas and beans it is the pod or fruit and the seed that has been subjected to selection, and therefore greatly modified; and it is here very important to notice that while all these plants have undergone cultivation in a great variety of soils and climates, with different manures and under different systems, yet the flowers have remained but little altered, those of the broad bean, the scarlet-runner, and the garden-pea, being nearly the same in all the varieties. This shows us how little change is produced by mere cultivation, or even by variety of soil and climate, if there is no selection to preserve and accumulate the small variations that are continually occurring. When, however, a great amount of modification has been effected in one country, change to another country produces a decided effect. Thus it has been found that some of the numerous varieties of maize produced and cultivated in the United States change considerably, not only in their size and colour, but even in the shape of the seed when grown for a few successive years in Germany.[31] In all our cultivated fruit trees the fruits vary immensely in shape, size, colour, flavour, time of ripening, and other qualities, while the leaves and flowers usually differ so little that they are hardly distinguishable except to a very close observer.
Variations of Apples and of Melons.
The most remarkable varieties are afforded by the apple and the melon, and some account of these will be given as illustrating the effects of slight variations accumulated by selection. All our apples are known to have descended from the common crab of our hedges (Pyrus malus), and from this at least a thousand distinct varieties have been produced. These differ greatly in the size and form of the fruit, in its colour, and in the texture of the skin. They further differ in the time of ripening, in their flavour, and in their keeping properties; but apple trees also differ in many other ways. The foliage of the different varieties can often be distinguished by peculiarities of form and colour, and it varies considerably in the time of its appearance; in some hardly a leaf appears till the tree is in full bloom, while others produce their leaves so early as almost to hide the flowers. The flowers differ in size and colour, and in one case in structure also, that of the St. Valery apple having a double calyx with ten divisions, and fourteen styles with oblique stigmas, but without stamens or corolla. The flowers, therefore, have to be fertilised with the pollen from other varieties in order to produce fruit. The pips or seeds differ also in shape, size, and colour; some varieties are liable to canker more than others, while the Winter Majetin and one or two others have the strange constitutional peculiarity of never being attacked by the mealy bug even when all the other trees in the same orchard are infested with it.
All the cucumbers and gourds vary immensely, but the melon (Cucumis melo) exceeds them all. A French botanist, M. Naudin, devoted six years to their study. He found that previous botanists had described thirty distinct species, as they thought, which were really only varieties of melons. They differ chiefly in their fruits, but also very much in foliage and mode of growth. Some melons are only as large as small plums, others weigh as much as sixty-six pounds. One variety has a scarlet fruit. Another is not more than an inch in diameter, but sometimes more than a yard in length, twisting about in all directions like a serpent. Some melons are exactly like cucumbers; and an Algerian variety, when ripe, cracks and falls to pieces, just as occurs in a wild gourd (C. momordica).[32]
Variations of Flowers.
Turning to flowers, we find that in the same genus as our currant and gooseberry, which we have cultivated for their fruits, there are some ornamental species, as the Ribes sanguinea, and in these the flowers have been selected so as to produce deep red, pink, or white varieties. When any particular flower becomes fashionable and is grown in large quantities, variations are always met with sufficient to produce great varieties of tint or marking, as shown by our roses, auriculas, and geraniums. When varied leaves are required, it is found that a number of plants vary sufficiently in this direction also, and we have zonal geraniums, variegated ivies, gold and silver marked hollies, and many others.
Variations of Domestic Animals.
Coming now to our domesticated animals, we find still more extraordinary cases; and it appears as if any special quality or modification in an animal can be obtained if we only breed it in sufficient quantity, watch carefully for the required variations, and carry on selection with patience and skill for a sufficiently long period. Thus, in sheep we have enormously increased the wool, and have obtained the power of rapidly forming flesh and fat; in cows we have increased the production of milk; in horses we have obtained strength, endurance, or speed, and have greatly modified size, form, and colour; in poultry we have secured various colours of plumage, increase of size, and almost perpetual egg-laying. But it is in dogs and pigeons that the most marvellous changes have been effected, and these require our special attention.
Our various domestic dogs are believed to have originated from several distinct wild species, because in every part of the world the native dogs resemble some wild dogs or wolves of the same country. Thus perhaps several species of wolves and jackals were domesticated in very early times, and from breeds derived from these, crossed and improved by selection, our existing dogs have descended. But this intermixture of distinct species will go a very little way in accounting for the peculiarities of the different breeds of dogs, many of which are totally unlike any wild animal. Such is the case with greyhounds, bloodhounds, bulldogs, Blenheim spaniels, terriers, pugs, turnspits, pointers, and many others; and these differ so greatly in size, shape, colour, and habits, as well as in the form and proportions of all the different parts of the body, that it seems impossible that they could have descended from any of the known wild dogs, wolves, or allied animals, none of which differ nearly so much in size, form, and proportions. We have here a remarkable proof that variation is not confined to superficial characters—to the colour, hair, or external appendages, when we see how the entire skeletons of such forms as the greyhound and the bulldog have been gradually changed in opposite directions till they are both completely unlike that of any known wild animal, recent or extinct. These changes have been the result of some thousands of years of domestication and selection, different breeds being used and preserved for different purposes; but some of the best breeds are known to have been improved and perfected in modern times. About the middle of the last century a new and improved kind of foxhound was produced; the greyhound was also greatly improved at the end of the last century, while the true bulldog was brought to perfection about the same period. The Newfoundland dog has been so much changed since it was first imported that it is now quite unlike any existing native dog in that island.[33]
Domestic Pigeons.