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.