composed of an internode of the rachis, a cupule and the 
lower glume. These structures become highly lignified 
as the fruit matures. Extensive experiments with maize- 
teosinte hybrids have demonstrated that the genes re- 
sponsible for the lignification occur on many, if not all, 
of the chromosomes of teosinte. Indeed, in segregating 
generations of maize-teosinte hybrids, it is difficult to find 
individuals, even the most maize-like, which do not ex- 
hibit some degree of lignification of the rachis, cupule 
and lower glumes. Consequently, when in archaeological 
cobs strong induration (lignification) of these structures is 
encountered, teosinte introgression is at once suspected, 
especially when such induration is accompanied by soli- 
tary spikelets and two-ranked spikes, both teosinte char- 
acters, as is the case in some specimens. Unfortunately, 
the seeds of archaeological maize are not viable and it is 
not possible to obtain direct and final proof through 
breeding experiments. However, all of the facts presented 
here are consistent with the hypothesis that there has 
been such introgression. 
Inasmuch as the hybridization of maize and Tripsacum 
has never been observed in nature and is, at best, rare, 
and since teosinte and maize do hybridize regularly in 
Guatemala and Mexico, we may, for the purposes of this 
discussion, assume that the prehistoric introgression rep- 
resented by these archaeological specimens comes from 
teosinte rather than from ‘Tripsacum and that this hy- 
bridization occurred in Mexico. We are left, however, 
with the possibility that maize has hybridized with local 
species of Tripsacum in the American Southwest and 
that the introgression involved is directly from 'Tripsa- 
cum, rather than indirectly through teosinte. 
Specific Gravity of Teosinte Derivatives and 
Archaeological Cobs 
Since the cobs of derivatives from maize-teosinte hy- 
[ 103 ] 
