N. Tabacum, and Lycopersicon may have been fairly late. 
If Annona cherimola, Chenopodium Nuttalliae and Sola- 
num tuberosum are all truly Andean in origin and _ pre- 
Columbian in Mexico and Guatemala, a good case might 
be made for direct transport over a considerable distance ; 
all are plants that thrive only in the temperate highlands. 
The plants which are definitely of lowland South 
American origin are few and of relatively little impor- 
tance. Ananas is almost certainly South American and 
pre-Columbian in Mexico, Manihot is of less certain ori- 
gin but also pre-Columbian in Mexico, although both 
may be relatively late. Arachis is certainly late and per- 
haps post-Columbian. 
While some of the doubtful domesticates may ulti- 
mately prove to be exotic, the bulk of the plants culti- 
vated in the Mexican area are indigenous, and the native 
agriculture has retained its character to a remarkable de- 
gree under the impact of European domination (81). It 
must be concluded that the complex of domesticated 
plants which developed in Middle America constituted a 
well balanced and stable system of agriculture, which is 
thereby resistant to extensive establishment of new cul- 
tivated plants (with domestic animals, it was quite other- 
wise). The inertia of cultural patterns is no doubt also 
involved, but many other areas have proven to possess 
far less stable systems. 
A really comparable list of the pre-Columbian culti- 
vated plants of the Andean region is not available, but 
would be of great interest. A nearly or quite equal num- 
ber of cultivated species could probably be enumerated 
for this area which is noted for its endemic crops. 
It has been argued, on competent grounds, that agri- 
culture has had several independent centers of origin in 
the New World (86, 175). While the origins and present 
distributions of the cultivated plants cannot alone throw 
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