geneous in their characteristics that it is impossible to 
classify all of them with respect to race. However, some 
of the cobs clearly resemble those of the race Chapalote. 
A series of these from the lower to the higher levels is 
shown in Plate III, B. 
Another type of cob thicker and more nearly cylin- 
drical in shape than those resembling Chapalote is illus- 
trated in Plate LV. These may be related to the Mexican 
race, Blando de Sonora, described by Wellhausen et a/., 
1952. Some of the kernels with colorless pericarp and 
floury endosperm illustrated in Plate III, C may also be 
related to this race. 
Changes in Kernel-row Number 
An increase in the diameter of the rachis provides a 
larger surface on which kernels can be borne and this 
results in either a higher kernel-row number or in larger 
kernels or in both. ‘Table LI shows that there has been 
a change in the kernel-row number from the lower levels 
to the higher. ‘The modal number in the lowest level is 
10 and in all higher levels, 12. The average row number 
of the cobs from successive levels, the lowest to the 
upper, is 10.6, 10.9, 10.2, 11.8, and 11.4. The increase 
in kernel-row number has, however, been relatively 
smaller than the increase in kernel size discussed below. 
Tue KERNELS 
Increase in Size 
There are 299 well preserved kernels in this collection, 
a much larger number than found in the 1948 material. 
The data in Table III show that there is a substantial 
increase in kernel length and width from the lower levels 
to the higher accompanied, however, by a decrease in 
thickness. The kernels from the lowest level are almost 
isodiametrical in their dimensions; kernels from upper 
levels tend to be longer, wider, and flatter. 
[ 10 ] 
