maize which have no counterparts in the maize of Mex- 
ico and Central America. The fact that Farquharson 
(12) found a variety of Peruvian corn to be especially 
effective in crossing with Tripsacum is of particular in- 
terest in this connection since it suggests the possibility 
that in some South American varieties the barriers to 
hybridization with Tripsacum may be weak or lacking. 
CONCLUSIONS 
A careful study has been made of the objections raised 
against the theory that many modern races of corn are 
the product of teosinte introgression, and of the new 
evidence which has been marshalled since the theory was 
first proposed. Nothing has been found which is clearly 
in conflict with the theory, whereas the body of facts in 
support of it is almost overwhelming. We regard this 
part of the tripartite theory as now so well established 
that it can safely be employed by corn breeders as a 
working principle in developing new methods for the 
improvement of corn. 
SUMMARY 
Five objections to the theory that many modern races 
of corn are the product of teosinte introgression have 
been examined and found to be unsupported by the 
available evidence. 
1. Hybridization between maize and teosinte is not 
rare but is common in many localities in Mexico and 
Guatemala and has presumably been going on for 
centuries. 
2. There is every reason to believe that this hybridi- 
zation has been accompanied by gene exchange. 
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