496 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1959 
pollen-receptive organs commonly known as the “silks.” These are 
covered with fine hairs and are admirably designed to capture wind- 
blown pollen (fig. 1, #). Thus corn, in contrast to the majority of 
cereals, is a naturally cross-pollinated plant. It is this feature which 
makes possible the production of hybrid corn, one of the most spec- 
tacular developments in applied biology of this century. 
Each silk represents a potential kernel and must be pollinated 
in order for that kernel to develop. The kernels themselves are firmly 
attached to a rigid axis, the cob, and are not covered, as are those 
of other cereals, by the floral bracts which botanists call “glumes” 
and which the layman knows as “chaff.” Instead the entire ear is 
enclosed, often quite tightly, by modified leaf sheaths, the husks or 
shucks (fig. 1, B). Thus, while in other cereals the kernels are 
protected individually, in corn they are covered en masse. The result 
is that cultivated corn has no mechanism for the dispersal of its 
seeds and hence is no longer capable of reproducing itself without 
man’s intervention. The very characteristics which make corn so 
useful to man render it incapable of existing in nature, and it is 
probable that corn would quickly become extinct if deprived of 
man’s protection. 
How, then, did corn’s wild ancestor differ from cultivated corn in 
ways which enabled it to exist in nature for thousands, if not 
millions, of years before man appeared on the scene? This is one 
of the questions which we hoped to answer by reconstructing the 
ancestral form. Our reconstruction is based in part upon fossil and 
archeological remains and in part upon genetic recombination of 
some of the primitive characteristics which still exist in modern corn 
varieties. 
FOSSIL CORN POLLEN 
The fossil evidence comprises a number of pollen grains isolated 
from a drill core taken from a depth of more than 200 feet below 
the present site of Mexico City. These were recognized as unusually 
large pollen grains of a grass by Paul Sears of Yale University and 
Kathryn Clisby of Oberlin College, who, in connection with charting 
climatic changes, were engaged in pollen studies of the drill core. 
The pollen was identified by Elso Barghoorn [3] of Harvard Uni- 
versity as that of corn, which has the largest pollen of any known 
grass. Although assigned to the last interglacial period and there- 
fore, on the basis of recent estimates, probably at least 80,000 years 
old, the fossil pollen is scarcely distinguishable in size, shape, and 
other characteristics from modern corn pollen (pl. 1, fig. 1). This 
fact leaves little doubt that the ancestor of corn was corn and not 
one of its two American relatives, teosinte or 7'ripsacum. 
