RACE VIII. Indian Frill-back.—In these birds the beak is very short, and the feathers of the whole body are reversed or turn backwards.
RACE IX. Jacobin.—These curious birds have a hood of feathers almost enclosing the head and meeting in front of the neck. The wings and tail are unusually long.
RACE X. Trumpeter.—Distinguished by a tuft of feathers curling forwards over the beak, and the feet very much feathered. They obtain their name from the peculiar voice unlike that of any other pigeon. The coo is rapidly repeated, and is continued for several minutes. The feet are covered with feathers so large as often to appear like little wings.
RACE XI. comprises Laughers, Frill-backs, Nuns, Spots, and Swallows.—They are all very like the common rock-pigeon, but have each some slight peculiarity. The Laughers have a peculiar voice, supposed to resemble a laugh. The Nuns are white, with the head, tail, and primary wing-feathers black or red. The Spots are white, with the tail and a spot on the forehead red. The Swallows are slender, white in colour, with the head and wings of some darker colour.
Besides these races and sub-races a number of other kinds have been described, and about one hundred and fifty varieties can be distinguished. It is interesting to note that almost every part of the bird, whose variations can be noted and selected, has led to variations of a considerable extent, and many of these have necessitated changes in the plumage and in the skeleton quite as great as any that occur in the numerous distinct species of large genera. The form of the skull and beak varies enormously, so that the skulls of the Short-faced tumbler and some of the Carriers differ more than any wild pigeons, even those classed in distinct genera. The breadth and number of the ribs vary, as well as the processes on them; the number of the vertebrae and the length of the sternum also vary; and the perforations in the sternum vary in size and shape. The oil gland varies in development, and is sometimes absent. The number of the wing-feathers varies, and those of the tail to an enormous extent. The proportions of the leg and feet and the number of the scutellae also vary. The eggs also vary somewhat in size and shape; and the amount of downy clothing on the young bird, when first hatched, differs very considerably. Finally, the attitude of the body, the manner of walking, the mode of flight, and the voice, all exhibit modifications of the most remarkable kind.[35]
Acclimatisation.
A very important kind of variation is that constitutional change termed acclimatisation, which enables any organism to become gradually adapted to a different climate from the parent stock. As closely allied species often inhabit different countries possessing very different climates, we should expect to find cases illustrating this change among our domesticated animals and cultivated plants. A few examples will therefore be adduced showing that such constitutional variation does occur.
Among animals the cases are not numerous, because no systematic attempt has been made to select varieties for this special quality. It has, however, been observed that, though no European dogs thrive well in India, the Newfoundland dog, originating from a severe climate, can hardly be kept alive. A better case, perhaps, is furnished by merino sheep, which, when imported directly from England, do not thrive, while those which have been bred in the intermediate climate of the Cape of Good Hope do much better. When geese were first introduced into Bogota, they laid few eggs at long intervals, and few of the young survived. By degrees, however, the fecundity improved, and in about twenty years became equal to what it is in Europe. According to Garcilaso, when fowls were first introduced into Peru they were not fertile, whereas now they are as much so as in Europe.
Plants furnish much more important evidence. Our nurserymen distinguish in their catalogues varieties of fruit-trees which are more or less hardy, and this is especially the case in America, where certain varieties only will stand the severe climate of Canada. There is one variety of pear, the Forelle, which both in England and France withstood frosts that killed the flowers and buds of all other kinds of pears. Wheat, which is grown over so large a portion of the world, has become adapted to special climates. Wheat imported from India and sown in good wheat soil in England produced the most meagre ears; while wheat taken from France to the West Indian Islands produced either wholly barren spikes or spikes furnished with two or three miserable seeds, while West Indian seed by its side yielded an enormous harvest. The orange was very tender when first introduced into Italy, and continued so as long as it was propagated by grafts, but when trees were raised from seed many of these were found to be hardier, and the orange is now perfectly acclimatised in Italy. Sweet-peas (Lathyrus odoratus) imported from England to the Calcutta Botanic Gardens produced few blossoms and no seed; those from France flowered a little better, but still produced no seed, but plants raised from seed brought from Darjeeling in the Himalayas, but originally derived from England, flower and seed profusely in Calcutta.[36]
An observation by Mr. Darwin himself is perhaps even more instructive. He says: "On 24th May 1864 there was a severe frost in Kent, and two rows of scarlet runners (Phaseolus multiflorus) in my garden, containing 390 plants of the same age and equally exposed, were all blackened and killed except about a dozen plants. In an adjoining row of Fulmer's dwarf bean (Phaseolus vulgaris) one single plant escaped. A still more severe frost occurred four days afterwards, and of the dozen plants which had previously escaped only three survived; these were not taller or more vigorous than the other young plants, but they escaped completely, with not even the tips of their leaves browned. It was impossible to behold these three plants, with their blackened, withered, and dead brethren all around them, and not see at a glance that they differed widely in their constitutional power of resisting frost."