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 grea