Barghoorn et a/ (4) identified fossil pollen grains of 
both corn and Tripsacum isolated from drill cores taken 
at a depth of more than 69 meters below the present site 
of Mexico City. Pollen grains thought to be those of 
teosinte were found also but only at levels above 3.6 
meters” which were probably laid down after agriculture 
had become established in the Valley of Mexico. Barg- 
hoorn et al also point out that teosinte pollen is interme- 
diate between corn and Tripsacum pollen, not only in its 
diameter but also, and perhaps more significantly, in the 
ratio of diameter of pore to the long axis. They conclude 
that this intermediate value is well in harmony with the 
postulated hybrid origin of teosinte. 
Virtually all of the archaeological corn so far studied 
shows that teosinte introgression, when it can be recog- 
nized, made its appearance only after pure corn had been 
grown for some time. Mangelsdorf and Smith (28) found 
no evidence of teosinte introgression in the lower levels 
of Bat Cave, although such introgression was conspicu- 
ous in the upper four levels. Cutler’s (10) descriptions 
and illustrations of prehistoric specimens from Tularosa 
Cave show that the typical corn from the lower pre- 
pottery levels is non-tripsacoid, while some of the speci- 
mens from the higher levels are strongly tripsacoid. 
The prehistoric corn from the lower levels of La Perra 
Cave in Mexico (25) had predominantly non-tripsacoid 
glumes, while that from the uppermost level had a high 
proportion of cobs with tripsacoid glumes. The most 
tripsacoid cob in the entire collection occurred in the 
highest level. 
Mangelsdorf and Lister (24) reported that tripsacoid 
cobs occur in the upper levels of Swallow Cave in north- 
” Weatherwax (53) is clearly in error in stating that teosinte pollen 
was found at depths of more than 150 feet. Randolph, the joint author 
of the same chapter, correctly states that no teosinte pollen was found 
at levels below 3.6 meters. 
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