to be a precursor of this modern but primitive race; 3) 
There is evidence of the introduction of an eight-rowed 
flour corn originally from South America; 4) There is 
evidence of hybridization with teosinte; 5) These several 
entities are finally blended into a modern race of maize, 
Cristalino de Chihuahua, which is grown in Chihuahua 
today and which has affinities with the maize of the 
American Southwest. 
The botanist is also indebted, in this instance, to the 
corn breeders of Mexico who, from strictly utilitarian 
motives, collected, classified, and described the living 
races of maize of that country. ‘Their monograph on the 
subject (Wellhausen et a/, 1952), with its detailed de- 
scriptions and excellent illustrations has furnished the 
clues to the identity of all of the different types of pre- 
historic maize collected from the five caves described 
above. 
The Principal Types 
The prehistoric cobs from these caves comprise five 
recognizable types, four of which still occur in the states 
of Sonora or Chihuahua. The remaining type is a now- 
extinct precursor of one of the four living types. The 
material from only one of the five caves, Swallow Cave, 
is sufficiently abundant and varied to show an evolution- 
ary series. The specimens from the other four caves are 
useful in furnishing corroborative evidence. 
Pre-Chapalote. The earliest intact cob, from Swallow 
Cave, comes from Level 13. This is a carbonized speci- 
men, 8.5 cm. long, having twelve rows with an average 
of nine kernels per row. In shape, it is quite similar to 
the earliest cobs from Bat Cave in New Mexico, dated 
by associated charcoal at 5000 years or more (Libby, 
1951), with which it is compared in Plate XX XIX, in- 
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