The Oregon ox, a cross between the Spanish and American breeds, is superior to either of the pure breeds. But it is the concentration in one animal of what might be the material of divers generations.
I once asked a Dutchess county farmer the cause of the great superiority of his crops of wheat over those of his neighbors, and his reply was that he always brought his seed from a distance, changed it often, and took good care not to let it intermix with the wheat of that region. The same, or, rather, greater results have attended the transportation of American seeds and plants to California, where a new soil and a new climate has produced upon all the staples of agriculture such an improvement as to astonish men who have made this branch of industry a study. It is the result of the migration of plants where there are no plants of the same character to intermix, and so deteriorate the race by crossing the breed. In trees the same law holds unchangeably. We produce fine fruit by inoculation and by grafting; but experience has taught us never to inoculate upon a grafted stem, but always upon a natural branch. As the Conquistadors selected the best-looking Indian women for the mothers of the Meztizos, so the fruit-raiser selects the best natural stems to inoculate with his artificial varieties of fruit. In this way we get better fruit by exhausting the root, and a whole race of plants are sometimes worn out by mixture from too close a proximity of the different families of the same genus. In the laws which Moses gave to the children of Israel, we find a provision against the evils of intermixtures in the precept: "Thy cattle shall not gender with diverse kind."