are more frequent in the Chalco region near Mexico City, 
where Mangelsdorf (1952) found that slightly more than 
one percent of the ‘‘maize’’ plants in a cultivated field 
were actually F) hybrids of maize and teosinte. Even the 
small colony of perennial teosinte in Jalisco, Mexico, is 
reported by Collins (1921) to have contained a plant 
resembling an F2 segregate of a maize-teosinte hybrid. 
Weatherwax (1935) mentions that, although maize- 
teosinte hybrids are continually coming into existence, 
the parent species do not blend because the intermediate 
forms have no survival value. Nevertheless, reciprocal 
introgression does occur between these species to the 
extent that it does not become deleterious. The result 
is the development of new races of teosinte and new races 
of maize. For example, the teosintes of Mexico usually 
have the same plant characters as the race of maize with 
which they commonly grow, while the maize from the 
same region shows evidence of teosinte introgression 
(Collins, 1921, and others). In this connection, all of the 
more productive races of maize in Mexico show evidence 
of teosinte introgression, some of which has come directly 
from outcrossing to teosinte (Wellhausen et a/., 1952). 
This beneficial effect of teosinte introgression is recog- 
nized by certain natives in western Mexico, as is evident 
from their practice of interplanting maizillo (almost cer- 
tainly teosinte) and maize for the purpose of improving 
the latter (Lumbholtz, 1902). 
Randolph also questions whether these hybridizations 
have led to any significant amount of teosinte introgres- 
sion in modern maize. It may be that local introgression 
has little influence in any one generation, but occurring 
over the centuries, it is almost certain to have some effect. 
Furthermore, Randolph’s view is inconsistent with the 
archaeological evidence. The oldest archaeological cobs 
from Mexico and southwestern United States have soft, 
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