2. The earliest prehistoric maize is a precursor of a 
living primitive race in Mexico, Chapalote. 
83. There was little evolution, except for a slight in- 
crease in size, in this race during a long period of time. 
4. At about 750+250 A.D., the maize of north- 
western Mexico began to change with explosive rapidity. 
5. This sudden evolutionary spurt is attributed to the 
introduction into the area of two new entities, an eight- 
rowed flour corn originally from South America and 
Tripsacoid maize which had become modified by teosinte 
introgression. 
6. These three entities combined to produce a new 
race, Cristalino de Chihuahua, which is assumed to be 
the product of genetic recombination, heterosis, and the 
mutagenic effects of teosinte introgression. 
7. All of the races of maize which occurred prehis- 
torically in northwestern Mexico are found archaeologi- 
eally or as living maize in the Southwestern United 
States. It is postulated that the highlands of northwest- 
ern Mexico served as a corridor for the northward diffu- 
sion of maize. 
LITERATURE CITED 
Anderson, E., 1944. Maize reventador. Ann. Mo. Bot. Gard. 31: 
801-315. 
——, 1947. Corn before Columbus. Pioneer Hi-Bred Corn Co., Des 
Moines, lowa. 
and F.C. Blanchard, 1942. Prehistoric maize from Cafion del 
Muerto. Amer. Jour. Bot. 29: 832-835. 
Arnold, J. R. and W. F. Libby, 1950. Radiocarbon dates. Institute 
for Nuclear Studies, University of Chicago, 
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