tulated that, since increased cob length is selected for in 
seed ears, teosinte hybridization is of positive selection 
value in the maize of Nobogame. 
Summary 
1. 
A detailed analysis of the maize fields was made in 
the Nobogame Valley in southwestern Chihuahua, 
where the pattern of cultivation for maize has not 
changed appreciably in the last one hundred years. 
The maize grown around Nobogame is a five month 
type belonging to the race Cristalino de Chihuahua. 
The teosinte belongs to the race Nobogame and is 
abundant along the margin of maize fields and grow- 
ing wild in the non-cultivated parts of the valley. 
Maize and teosinte are not seasonally isolated as they 
are at most other sites where the two occur together. 
The mid-flowering times overlap in August and maize 
xXteosinte hybrids occur naturally. ‘Teosinte pollen 
is sufficiently abundant at flowering that many polli- 
nations on maize cobs are by a teosinte parent. Seed 
ears of maize have been shown to be contaminated by 
teosinte pollen resulting in the actual planting of 
maize X teosinte hybrids by the cultivator. 
The cobs of the maize planted in the valley show 
pronounced signs of tripsacoid germ plasm such as 
induration of the lower glume and a straight rigid 
cob. These characteristics are attributed to the intro- 
gression of tripsacoid genes via direct hybridization 
with teosinte foliowed by subsequent introgression 
from maize and teosinte backcross progeny. ‘The 
maize backcross progeny are usually harvested while 
the teosinte backcross progeny are usually left stand- 
ing in the field. Although introgression is reciprocal, 
[ 307 ] 
