semble the present day maize from the Southwest (Plate 
XXIII, cob I). 
Summary 
1. The method of scoring for teosinte introgression 
according to the degree of induration has been used to 
study the archaeological record of the role of such intro- 
gression in the evolution of 2575 cobs found in five suc- 
cessive strata in Cebollita Cave in New Mexico. 
2. The evolutionary sequence starts at Level 5 with 
a pure type of Chapalote, the indigenous race from this 
part of North America. Identification of this original 
Cebollita maize as Chapalote was possible because its 
morphological details were perfectly preserved by car- 
bonization. 
3. Aftera period of abandonment of the cave most of 
the maize in Level 4 changed abruptly to a highly Trip- 
sacoid type of Chapalote which was becoming prevalent 
in the Southwest. Some of the more Tripsacoid of these 
specimens resembled, in induration and appearance, seg- 
regates from experimental hybrids between maize and 
teosinte, while other specimens remained identical to the 
original pure type. 
4. The immediate effect of the teosinte introgression 
was to cause a marked reduction in average cob-size to 
the lowest values of the site. 
5. Although advances to higher Levels (8, 2, 1) were 
marked by a progressive decrease in the indurative effects 
of this introgression, the variability in cob size which was 
introduced by the introgression continued to increase. 
For cob diameter, increases in variation cease at Level 
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