no less subject to the occurrence of spiral rows than ears 
with pairs in odd number. 
Finally, in varieties of this kind there is not the pre- 
ponderance of ears whose rows of paired spikelets are in 
even numbers, so commonly found in North American 
varieties. Ears with ten, fourteen and eighteen rows are 
as frequent as ears with eight, twelve and sixteen rows. 
This, like the presence of spiral cross-rows, is character- 
istic of both prehistoric and modern varieties as is shown 
by the following frequency distribution, which includes 
modern ears from Isla del Sol in Lake Titicaca and pre- 
historic ears excavated by Dr. Julio Tello from the Para- 
cas Necropolis in Peru and by Dr. Junius Bird from 
Arica, Chile. Data on row numbers in the last named 
collections were kindly furnished by Dr. Edgar Ander- 
Collection Number of Rows of Grain Total 
10. 1214. 16-238" 620. 722 
Isla del Sol, Bolivia 5 12 19 9 5 50 
Paracas, Peru (Prehistoric) 4 10 5 2 2 1 24 
Arica, Chile = 1 14 24 10 2 51 
son. The situation is the same in all three cases; there 
is no deficiency of ears in which the number of pairs of 
rows is odd, indeed the modal number in all cases is 
fourteen. 
Discussion AND CONCLUSIONS 
The conclusion that there are two morphologically dis- 
tinct types of maize ears is not new. Mangelsdorf and 
Reeves (18) have previously suggested that the maize 
varieties of America comprise two more or less distinct 
groups: (1) ‘‘pure’’ maize which traces its descent directly 
from the original wild corn; (2) Tripsacum-contaminated 
maize resulting directly or indirectly from the hybridiza- 
tion of maize and Tripsacum. It was assumed that the 
differences between these two groups were reflected in 
[ 67 | 
