trogression in maize cobs as exists in Nobogame. The 
abundance of Fy, hybrids is comparable to Chalco, where 
several researchers have studied maize X teosinte hybrids 
(Lopez y Para (1908), Collins (1921), Bukasov (1926, 
1930), Mangelsdorf (1952), and Wilkes (1967)). Unlike 
the region around Chalco, however, teosinte is not lim- 
ited to the cultivated fields. ‘Teosinte also occurs in dense 
stands along the streams and in areas protected from 
grazing on the surrounding hills. 
Although all the fields had been harvested at the time 
of the field work (November), careful investigation indi- 
‘rates that maize Xteosinte hybrids are present in the 
fields proper, but not as abundant as they are on the 
margin of the maize fields or in the willow thickets along 
the stream. When maize X teosinte hybrids are encoun- 
tered in the maize fields of Mexico, it is usually pre- 
sumed that they are from teosinte fruit-cases containing 
hybrid seed which were naturally disseminated in the 
tield. In Nobogame, the female parent of the teosinte x 
maize hybrids is sometimes maize and thus the hybrids 
are often planted in the field. 
Teosinte introgression 
The evidence of teosinte introgression into maize Is 
clearly seen in maize cobs throughout those parts of the 
valley where teosinte is most abundant. At harvest time 
the entire ear is brought to the granary, and for several 
weeks thereafter the ears are left to air dry in large piles 
around the courtyard. A sector of each of twenty piles 
representing twenty distinct fields of eight cultivators 
was studied. 'wenty-five cobs were separated from the 
pile and shelled. Approximately + of all the cob samples 
expressed the tripsacoid characteristic of a pronounced 
induration of the rachis and lower glume. All of the 
piles possessed tripsacoid cobs (Wilkes, 1968), although 
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