to the great antiquity of this agricultural tendency, while archeology gives equally vivid testimony to the same antiquity and diversity of the prehistoric civilizations of America. From the mounds of Ohio to the equally remarkable ruins of Patagonia, the American continents and islands are, as it were, dotted with remains of rudimentary civilizations which must have required centuries and millenniums to rise from surrounding savagery, culminate and perish. The constructive arts by which the existence of these vanished peoples is made known took the most diverse forms; some made mounds, some expended their energies upon huge carvings on high inaccessible rocks, some dug devious underground passages, some set up monoliths and carved statues, and some built massive pyramids, temples and tombs, while still others are known only from their pottery or their metal work. In civilization, as in agriculture, the tropics of America stand in striking contrast to those of the old world. Here men of the same race showed great diversity of plants and arts; there races are diverse, while arts and staple food-plants are relatively little varied. The early civilizations of the eastern world resembled some of the primitive cultures of America more than these resembled each other.
The American origin of agriculture is thus not doubtful, since not merely one, but several, agricultures originated in America. The same cannot be claimed for Asia and Africa, where only root-crops shared with America attained a wide distribution, an indication that they reached those continents before the uses of the similar indigenous plants had been discovered.
The American habit of eating roots was not a simple and direct transition from the use of fruits, which are commonly supposed to have been the primitive food of man. The more important and the more ancient of the distinctively old world root-crops, onions, leeks, garlic, carrots, radishes and turnips, are eaten, or are at least edible, in the raw state, while in America there seems to be no indication that the natives used any of their root-crops in this way. Some of them, such as the sweet potato, the artichoke and the 'sweet cassava,' can be eaten raw, but throughout the tropics of America the Indians, like the Chinese, prefer everything cooked. This habit must have been adopted very far back to have made possible the obviously ancient domestication of Manihot (cassava), Colocasia (taro) and Xanthosoma (yautia), since the fleshy underground parts of these plants contain substances distinctly deleterious until disintegrated and rendered harmless by heat. The same may have been true of the sweet potato, since the fleshy roots of its uncultivated relatives are strongly purgative. Several of the yams, both wild and cultivated, are also poisonous in the raw state.