Page:Popular Science Monthly Volume 61.djvu/502

496 now generally agreed that the tribes, languages and arts of the American Indians are of truly indigenous development, while it is held, on the other hand, that the Polynesians migrated eastward from Asia, but without reaching the shores of America. That these two suppositions can not both be true is apparent as soon as it is known that there has been a transfer of numerous cultivated plants between Polynesia and America, and other agricultural facts enable us to judge between the inconsistent theories. Since it is reasonable to suppose that the food plants which the Polynesians shared with the tropical peoples of both continents were carried by them across the Pacific, it is also reasonable to seek the origin of these widely distributed species on the continent which gives evidence of the oldest and most extensive agricultural activity, and to the question in this form there can be but one answer. The agriculture of the old world tropics is adequately explainable by the supposition that it was brought by the Polynesians, since the root-crops of the Polynesians were also staples of the old world tropics. This proposition would not apply to America, where, in addition to the sweet potato, yams, yam-bean (Pachyrhizus) and taro, which crossed the Pacific, the aborigines also domesticated a long series of rootcrops—Manihot (cassava), Maranta (arrowroot), Calathea (lleren), Solanum (Irish potato), Xanthosoma (several species), Oxalis (Oca), Carina, Tropæolum, Ullucus, Arracacia, Sechium and Helianthus (artichoke), all of considerable local importance.

The simplest of cultural methods, propagation from cuttings, was applied to all these root-crops and has been in use for so long a period that several of them have become seedless. With equal uniformity the distinctively old world root-crops are grown from seed. American root-crops belong to at least twelve natural families, and the only important old world addition to the series is the mustard family, a distinctly temperate group, the cultivated members of which have not been greatly modified in domestication, and are still known in the wild state.

This apparent superfluity of American root-crops is explainable by the fact that different plants were independently domesticated in different localities, which means also that conditions favorable to the development of agriculture were very general among the natives of America. That most of these plants are not known in the wild state testifies also