evidence from modern maize-teosinte derivatives, that 
much of the variation in modern maize is the product not 
only of recombination of genes from the two species, but 
also from the mutagenic effects of teosinte germplasm in 
maize. Similarly, some of the increased variation in the 
Cebollita maize may be the result of a mutagenic effect 
of teosinte germplasm. 
Level 2 Maize 
Proceeding to the next Level (2), the same trends con- 
tinue: teosinte introgression decreases while average 
sar-size increases. ‘The extremes in cob-length and cob- 
diameter held about the same as those of the previous 
level (Table IL). But in the case of cob-length, the vari- 
ous categories became more equally represented with the 
result that the standard deviation or variability increased. 
As mentioned previously, the longest cobs are apparently 
a product of maize-teosinte heterosis. The fact that cob 
length did not decline with the apparent reduction in 
introgression at these higher levels might be explained 
in terms of a selective elimination of deleterious factors 
from teosinte and/or a buffering against the effects of 
such factors while beneficial factors involved in maize- 
teosinte heterosis were retained and blended into the 
evolving population. 
Level 1 Maize 
The cobs from the uppermost level represent the final 
evolutionary product from this site. Although the actual 
quantity of cobs was less than ten per cent of that from 
any previous level, it yields some of the longest and best 
specimens. ‘These superior ears represent a combination 
of butt fasciation descended from the original Chapalote 
together with the more lignified and heterotic products 
of teosinte introgression. Some of these specimens re- 
[ 176 ] 
