It is interesting to note that the cob/rachis index in 
the Bat Cave maize varies from 3.0, a condition in which 
the rachis is slender and the glumes are prominent, to 
1.2, a condition in which the rachis is large and the 
glumes are relatively short. The cob/rachis index is, 
however, relatively constant through the three lower 
strata, but shows some change in the upper three. It is 
of particular interest to note that, although new types 
with a low cob/rachis index appear in the upper strata, 
the original types with a high index, though becoming 
somewhat less frequent, do not disappear. If human se- 
lection had been operating in favor of the lower alleles 
at the T'u-tu locus, it certainly had not, in the period rep- 
resented by the uppermost strata, succeeded in com- 
pletely eliminating the higher alleles. There has, as in 
other characteristics, been primarily an increase in the 
range of variation. 
Rows of Grain. There has been no constant change 
in the number of rows of grain from stratum to stratum. 
An increase in the circumference of the cob should re- 
sult either in an increased number of rows of grain or in 
wider grains. It will be shown later that there has been 
a progressive increase from stratum to stratum in the 
average width of the grains. Similarly, although it is not 
clearly revealed by the summarized data, there has been 
an increase in the number of rows as a consequence of the 
increase in the circumference of the rachis. Indeed, the 
principal variation in the two lower strata has been con- 
cerned largely with the diameter of the rachis, the prom- 
inence of the glumes and the number of rows. Of 41 
ears which were scored for both row numbers and 7'v 
allele, 16 were classified as fourth-tunicate, 8 as half- 
tunicate and 17 as intermediate between these two con- 
ditions. The average row numbers of these three groups 
is shown below. 
[ 221 | 
