Page:Scientific Monthly, volume 14.djvu/27

scrofa) and the Indian wild boar (Sus Cristata) but almost every region of the earth has its native species more or less closely allied to domesticated swine.

One could extend this recital of the origin of tame animals to show that in the case of sheep there are at least six wild species which could have been drawn upon and a host of more distantly related forms and with cattle domesticated forms are classified in two species, European and East Indian, and any number of closely allied wild species. The horse is rather unique in being the only animal with no closely related wild congeners from which it could be re-established in case the horse became extinct. Either the horse has had a comparatively simple origin or else it has been cared for so long that its prototypes have been lost.

Although much of the history of domesticated races is largely surmised there can be no doubt but that the intercrossing of different species from separated regions has played a very important part in their great alterations to suit the needs of man. Desirable qualities existed in several forms of allied animals in different regions. Tribal migrations and commercial intercourse furnished the means for bringing them together and as far as they were sexually compatible crossing undoubtedly was utilized to combine good features; and also the crossing and resulting variability brought out new possibilities not before realized. How else can one account for the great flexibility of domesticated races as contrasted to wild species?

The same occurrence of species-hybridization is largely at the bottom of the development of cultivated plants. Some forty-two distinct species and sub-species of cotton have been described from both the Eastern and Western Hemispheres. Many of these are cultivated in various parts of the world. In this country 99 per cent, of the cotton grown is the short staple upland type and the remainder is the long fibered Egyptian or Sea Island cotton, so called as it was grown successfully only on the islands off the South Atlantic coast, and parts of the mainland. It is now grown in Egypt and in the irrigated valleys of the southwest.

Authorities differ as to the origin of the cultivated cottons. Cross-pollination of the plant is easily effected by insects and hybridization between species introduced into new regions has certainly taken place. Watt considers upland cotton to be various hybrids between Gossypium herbaceum, G. mexicanum and G. hirsutum. The former is the old world form which probably originated in north Arabia and Asia Minor. The other two species are natives of the southern United States, the West Indies and Mexico. Sea Island cotton is generally considered as G. barbadense originating in Barbados or other West India islands but Watt is convinced that it too has had a mixed beginning. He considers