be of Andean origin. Though the species of cotton in 
Mexico is not the same as that of the Andean area, it is 
believed that they both diverged from a common ancestor 
under cultivation and that cotton culture in the New 
World stemmed from the Andean area. Two or three 
plants may be considered as having diffused from lowland 
South America under cultivation. There remain eight 
species which the author hesitates to assign to any of 
these areas. All, of course, are now very widespread, and 
this portion is not completely comparable to the rest of 
the list, which includes many local types. It may be ex- 
pected that several, if not most, will prove to be natives 
of the Mexican region. 
Mangelsdorf and Reeves (129), after a survey of the 
American cultivated plants, conclude that there had been 
no direct interchange of crop plants between the Andean 
and the Middle American areas, but that both regions 
had received some plants from lowland South America, 
thus accounting for the relatively few species that occur 
in both areas. Hutchinson, Silow and Stephens (105), 
on the other hand, hypothesize an early exchange of 
plants between these two centers, with little or no sub- 
sequent exchange. It is doubtful that ‘‘direct’’ transfer 
of plants between Mexico and the Andes occurred at any 
time before European contact. Plants traveled by grad- 
ual diffusion and those which occurred in both regions 
were mostly the ones which could and would be grown 
in the intervening areas. The indigenous tuber crops of 
the Andes would do poorly at lower elevations, and there 
would seem to be little incentive for their cultivation 
where Manihot and Ipomoea were both available and 
better adapted. The different Andean plants in Mexico 
were probably not of contemporaneous introduction. 
Cotton was clearly early, as was probably Chenopodium, 
if it is Andean. Nicotiana rustica was much earlier than 
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