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28 root habits to reach the moisture in their very arid fields. These are, no doubt, but suggestions of many other adaptations awaiting discovery and which present very interesting chronological problems.

The art of irrigation was known from Arizona to Chile, and in Peru was carried out on a scale scarcely equalled by modern nations. The remains of aqueduct systems in the Andes show such genius and organization that our respect for the native American rises to a high point.

The alternate of maize, cassava, or manioc, deserves special consideration. Though requiring a more tropical habitat than maize, it also requires a fairly dry, sandy soil. At the period of discovery it was found in the West Indies, Central America, and even in Florida. The poisonous nature of the juice leads to a mode of preparation described fully in the special literature. The essential procedure is to grate the pulpy parts and squeeze them in a basketry press called a tipiti. The pulp is then made into cakes and heated to drive out the remaining volatile poison, finally giving cassava bread, which is a staple food.

If we now take a general view of the data at hand it appears a fair assumption that the prevailing type of agriculture was developed by a centrally located highland people and thence diffused, without essential modification, both to the north and to the south. While our experience shows that the art could have been extended farther to the extremes of the continent, it is doubtful if the aboriginal type could have been greatly extended without fundamental changes. In other words, the more primitive hunting tribes of the north and south borrowed the trait one after the other, so far as their habitat permitted.

In connection with this discussion of cultivated plants some note should be made of aboriginal narcotics. The best known are tobacco and coca, both extensively cultivated in aboriginal times, as shown on the distribution map (Fig. 8). The narcotic element in coca is cocaine, a modern derivative.