Zeevaert, the engineer in charge of the core sampling, by 
Professor Paul Sears of Yale University for palynological 
studies to chart climatic changes as they might be revealed by 
changes in frequencies of pollen of various species especially 
of pines indicating a drier, cooler period: oak and alder a 
warmer, moister one and fir a cooler, moister one (/2). In 
analyzing the pollen found in the cores, Sears’ associate, Mrs. 
Kathryn Clisby, observed in the lower levels of the profile, 69.3 
- 70.5 meters, a number of indubitable grass pollen grains that 
seemed too large to be identified as those of ordinary grasses. 
Thinking that these might be the pollen grains of teosinte, Sears 
and Clisby obtained from Mangelsdorf pollen of several var- 
leties of teosinte. When it became apparent that some of the 
fossil pollen grains were larger than those of teosinte, Sears, 
Clisby and Mangelsdorf agreed that these might be pollen 
grains of corn and decided to send the cores to Elso S. Barg- 
hoorn, a paleobotanist at Harvard, for further study. Barg- 
hoorn and his then graduate student Margaret Wolfe made an 
intensive study of the fossil grains, macerating out additional 
ones from the core centers to eliminate possible surface con- 
tamination and comparing them in size and also in the ratio of 
the pore diameter to the long axis with pollen of fourteen 
varieties of modern corn, three of teosinte and eight of Tripsa- 
cum, amore distant relative of corn which, like teosinte, oc- 
curs widely in Mexico. 
The results of these comparisons show that, although there is 
an overlapping in size frequencies between the pollen grains of 
corn and those of teosinte, some of the fossil pollen grains are 
much too large to be classified as teosinte. We (/3) concluded 
that the large fossil pollen grains were almost certainly those of 
a wild maize once growing in the Valley of Mexico, well before 
the beginnings of agriculture in Middle America, and this es- 
sentially established two important facts: 
I. Corn is an American plant and not one of Asiatic 
origin. 
. The ancestral form of cultivated corn was corn 
and not teosinte. 
i) 
The conclusion with respect to corn’s American origin 
240 
