326 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1919. 
cupied by larger and more advanced communities, because denuda- 
tion is more extensive and complete. Large Indian towns in Central 
America are surrounded by belts of deforested grasslands, and many 
districts that were centers of ancient populations are now wunin- 
habited. 
Assuming that the ancient people lived under the same conditions, 
grew the same crops, and used the same system of agriculture as the 
native populations of recent times, it is reasonable to infer that the 
consequences of deforestation and denudation were the same in the 
past as in the present, and that the same difficulties were encountered 
in maintaining the food supplies in populous regions. The ancient 
cities and sculptured monuments of Central America show that 
relatively large, centralized communities must have existed, and limi- 
tations of the native system of agriculture may explain why the 
ancient centers of population were abandoned. 
To recognize the limitations of the primitive systems is not with- 
out practical bearing, in pointing to the danger of over-balanced 
urban activity and congestion without corresponding development 
of agriculture. Wider exploitation of natural resources by industrial 
nations is made possible by modern facilities of communication, but 
the biological limitations of production are to be recognized, as with 
the primitive milpa system. Although cultivation is more con- 
tinuous where tillage methods are used, systems of agriculture that 
do not maintain the fertility of the soil are essentially nomadic and 
predatory. More permanent agriculture and more rational distribu- 
tion of populations are problems to be faced. Agriculture is the 
root of civilization, and the plant withers if the root decays. 
