(Figure 8 C) over the entire ear except for a small por- 
tion at the base where there was a slightly irregular ar- 
rangement, based apparently on nine rows. Some of the 
progeny of these ears had 9 rows of grains and of alicoles. 
A second novelty is the potential increase in number 
of rows of grains which is possessed by the Coroico race. 
If the ear is condensed longitudinally or spread out lat- 
erally, the grains and the alicoles assume the position of 
those in ordinary ears with the eight rows of. alicoles 
arranged to form sixteen rows of grain. There is good 
evidence that this change occurs, for ears from localities 
near Coroico usually have row numbers near 16 or less 
(Plate XX XV, E, F,G), and have a high degree of tes- 
sellation or interlocking of the grains. 
Is it possible that ears with row numbers less than 16 
are affected by contamination or by selection for larger 
and softer grains which also reduced row number? The 
oldest South American prehistoric ears have 14-16 rows 
of small grains while later prehistoric ears have fewer 
rows of larger and softer grains or may have more rows 
and still have small hard seeds. This probably represents 
the development of maize for special uses from an orig- 
inal 16-rowed type, one type for boiling, parching or 
grinding, the other for popping. It is significant that 
much of the oldest maize in South America bears the 
paired female spikelets upon a pedestal similar to that 
in Coroico maize. 
Prehistoric and pop corn are not included in this paper 
because they present special problems. Pop corn has 
primitive types as well as recent developments which 
owe much of their character to mixture with the races 
described here. In prehistoric maize there is much of the 
same problem, with some primitive types which persisted 
until quite recently and other types which may either 
represent developments in the region where their remains 
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