a cob has bony rachis tissue, bony lower glumes, upper 
glumes lacking in venation and a hispid cupule, it is al- 
most certainly a product of teosinte introgression. If it 
has some of these characteristics, but not all, it is assumed 
to represent teosinte introgression of a lower order. 
In each of the first two strata there was only one cob 
which showed evidence of strong introgression of teo- 
sinte. These cobs were atypical of the strata in almost 
all of their characteristics and are probably ‘‘intrusions, ”’ 
a convenient term employed by archaeologists to describe 
specimens which are found in any part of a cultural de- 
posit in which they obviously do not belong. With rats 
and other rodents digging burrows in ancient refuse 
heaps, it is almost inevitable that a specimen from a high- 
er stratum will occasionally find its way into a lower. In- 
trusions, therefore, have a real basis in fact and are not 
merely a device for conveniently explaining exceptions. 
Cobs showing evidence of teosinte introgression occur 
in somewhat greater frequency in Stratum III, but are 
not common. These, too, may be intrusions or they may 
result from the fact that the line of demarcation between 
the strata is entirely arbitrary. In any case, not until 
Stratum IV is reached can we be certain that teosinte- 
contaminated maize has become a conspicuous part of 
the population. 
The amount of teosinte introgression is greatest in 
Stratum V and drops off perceptibly in Stratum VI. 
Two possible reasons for this decline come to mind at 
once. The first is that introductions of non-tripsacoid 
maize from other regions have ‘‘diluted’’ the teosinte 
germplasm; the second is that some of the more obvious 
effects of teosinte have become modified through the de- 
velopment of an appropriate modifier complex. Since 
there is no clear-cut evidence of an introduction of non- 
tripsacoid maize on a large scale, the second possibility 
Bryal 
