Page:Popular Science Monthly Volume 61.djvu/500

494 the ancient agricultural peoples of the Tropics. At present we have only incomplete and scattered data collected incidentally by missionaries, travelers and professional botanists who did not appreciate their opportunities from the agricultural point of view. But even these miscellaneous facts are often of unexpected interest. Thus, we know that in Central America the use of leguminous shade-trees in cacao plantations was adopted by the Spanish colonists from the natives who furnished even the name 'mother of cacao,' by which the species of Erythrina and other leguminous trees are still known in Spanish America. The Indians, of course, were not aware that the roots of the Leguminosas develop tubercles for the accommodation of bacteria able to fix atmospheric nitrogen; they believed that the 'madre de cacao' supplied water for the roots of the cacao, a fanciful idea still credited by many planters of cacao and coffee. In the Pacific we encounter a similar fact with reference to the yam bean (Pachyrhizus), a leguminous vine with a fleshy edible root. The natives of the Tonga Islands no longer cultivate Pachyrhizus for food, but they nevertheless encourage its growth in their fallow clearings in the belief that it renders them the sooner capable of yielding large crops of yams. Such anticipations of the results of modern agricultural science are of extreme interest, but it is still uncertain whether similar knowledge exists in other archipelagos of the Pacific, or on the American continent where Pachyrhizus probably originated. The botanists report it as 'a common weed in cultivated grounds,' and we learn further that in the absence of better material, the people of Fiji use the fiber for fish-lines, and that the plant sometimes figures in an unexplained manner in their religious ceremonies.

Our knowledge is far from complete regarding even the present distribution of the principal tropical food plants, but the need of further investigation should not obscure the striking fact that several of the food plants with which the Spaniards became acquainted in the West Indies were also staple crops on the islands and shores of the Pacific and Indian Oceans, and even across tropical Africa.

Ethnologists who might have appreciated the bearing of this have passed it by because of the absence of maize or Indian corn among the Polynesians. But in addition to the unreason of accepting negative evidence as an offset for positive fact, two pertinent considerations have been overlooked, first, that most of the varieties of maize do not thrive in the humid climates of the equatorial islands, and, second, that maize was found by Captain Moresby in cultivation with yams, sweet