above: that the unit of development is a pair of rows of 
spikelets. 
3. Reeves (15) has also pointed out that with a spiral 
phyllotaxy the rachis segments are probably hexagonal, 
fitting together ‘‘like the engaged teeth of mechanical 
gears.’’> With an odd number of rows of paired spikelets 
there is a physical necessity for some kind of distortion. 
Either the rachis segments must change shape or the ear 
must become twisted. 
The net result of these various factors, which are close- 
ly related to each other, is that there is a strong tendency 
for rows of spikelets to occur in even numbers. When 
they do occur in odd numbers there is a strong tendency 
for the ear to be twisted. Stated in still another way ; 
there is a strong tendency for ears of maize to be bal- 
anced and symmetrical, rather than unbalanced and 
asymmetrical 
The above discussion applies especially to ears with a 
rigid spiral phyllotaxy and indurated tissues, the kind of 
ear derived from maize-teosinte crosses and the kind pre- 
sumably resulting in nature from Tripsacum contamina- 
tion. What of “‘pure’’ maize, with its whorled phyllo- 
taxy and random arrangement of spikelets, with respect 
to these phenomena! Many varieties of Bolivian and 
Peruvian maize, both prehistoric and modern, have rows 
of grain more strongly spiral than those of the twisted 
ears of North American varieties. Extreme forms, as 
Anderson (unpublished) has noted, have ‘‘spiral cross- 
rowing in two directions, like a pine cone.’’ But this 
condition in Bolivian and Peruvian maize does not give 
the impression of abnormality. Like the pine cone with 
which it has been compared, it appears to be perfectly 
normal. Furthermore the occurrence of spiral rows in 
Bolivian and Peruvian maize is usually independent of 
row number. Ears with pairs of rows in even numbers are 
[ 66 | 
