another, but is remarkably constant within the races 
(Plates XX XV-XXXVII). It has not been studied as 
well as it should have been because it is dependent upon 
numerous factors and measurements and comparisons are 
difficult to make. One of the peculiarities of Tripsacoid 
maize, which has high numbers of chromosome knobs in 
Central and North America, is the long naked cob-tip, 
which is also found in some Guarani maize of Paraguay. 
Andean maize and Guatemalan highland maize with few 
chromosome knobs have the tip of the ear completely 
covered by grains. Ears of Longfellow flint and some 
ears from the Iroquois tribes of New York also have this 
grain-covered tip. 
Anderson (1944) has indicated a correlation between 
high condensation index and high row number in North 
American maize, and it is probable that the high row 
number in Bolivian sweet (Plate XX XVII, G, H) is 
brought about by the same fasciation which increased 
the number of tassel branches. Row number is dependent 
upon many factors and little is known about the manner 
in which it is regulated. It is, however, relatively con- 
stant within each race (Table I) and with the exception 
of the two lowland races, Coroico and Guarani, usually 
does not vary much within a race. 
Mangelsdorf has shown that there probably are two 
types of arrangement for the ear and tassel (1945). His 
studies were made on tassels and tunicate ears of Guarani 
maize. More recently a method! of distinguishing be- 
tween the paired spikelets of an ear has been developed 
and the ears examined support his contention that Trip- 
sacoid types tend to have a systematic arrangement while 
’ Plate XXXIV shows an alicole of a maize ear after the lower glume 
has been cut away and the upper glume and the parts above it torn 
off. Note that one spikelet arose from a hair-fringed callus located in 
the bottom of the alveolus while the other was attached to the side 
of the alveolus at a point farther from the center of the cob. 
[ 271 ] 
