other possibility, viz: a comparison of the ratio in size 
which exists between the pore (including the annulus) of 
the pollen grain and that of its long axis (Text Fig. 2). 
In order to establish these ratios and to determine 
their constancy, if any, approximately 50 additional 
grains were measured from each preparation with respect 
to these dimensions. In the case of the fossil grains all 
those exhibiting intact pores were measured. The meas- 
urements were averaged and the ratios computed from 
the averaged value for each species. The results showed 
encouraging consistency, the ratio of pore to long axis 
being an unexpectedly conservative value, and, more 
important to the problem at hand, significantly different 
among the three species in question. The numerical val- 
ues computed are shown in Table II. 
Although the data are limited to approximately 1000 
pollen grains, the differences are so consistent, both with 
respect to individual grains and averages as well, that the 
pore-long-axis ratio appears to be a valid means of al- 
ways distinguishing maize pollen from that of Tripsa- 
cum, and in some instances from that of teosinte. It may 
be noted also in connection with this analysis, that teo- 
sinte, a postulated hybrid between maize and Tripsacum 
(Mangelsdorf and Reeves, 1939), shows an intermediate 
value both in overall size, and perhaps more significantly, 
in its pore-ratio. The intermediate value is well in har- 
mony with the postulated hybrid origin of teosinte. 
Fossil pollen grains resembling maize, teosinte and 
‘Tripsacum in size and in their pore-axis ratios occur in 
the upper levels of both the Madero and Belles Artes 
Text Fie. 1 Comite eee | Dine shai the distribution il 
frequency of maize, teosinte and Tripsacum in samples studied from 
the Madero and “se Belles Artes cores. Note that the Belles Artes 
core was sampled throughout, the Madero core only to a depth of 
5 meters. Numbers in parentheses indicate the number of individ- 
ual grains. Depth is indicated in meters. 
[ 232 | 
