tioned, that the wild progenitor of maize was a lowland 
plant. Whatever may have been the nature of the orig- 
inal wild maize, it has given rise under domestication to 
varieties differing widely in their adaptation. ‘Those in- 
troduced into Guatemala were apparently high-altitude 
varieties; at any rate only varieties adapted to high alti- 
tudes have survived the encroachment of the 'Tripsacoid 
types. 
The importance of differences in altitude as natural 
barriers to promiscuous hybridization is emphasized by 
the situation in Huehuetenango. Here maize varieties 
with extremely low knob numbers, the lowest encoun- 
tered in Guatemala, are found in Santa Eulalia while only 
eleven and fifteen miles away, at Jacaltenango and San 
Antonio Huista respectively, are found maize varieties 
with extremely high knob numbers. ‘These localities 
though not far apart in distance are separated by more 
than 3000 feet in altitude. To one who has traveled in 
Guatemala and been transported from the steaming trop- 
ics near sea level to chilly mountain passes above the 
clouds in a distance of twenty-five miles by road, the ef- 
fectiveness of this barrier is not difficult to appreciate, 
especially when it is associated, as it is in many cases in 
Guatemala, with actual physical barriers. 
Size and shape of ear 
No more than a casual inspection is required to show 
that in this collection, number of knobs is associated with 
size and shape of ears. Among the varieties with low- 
knob numbers are many ears with a pyramidal shape, the 
diameter at the butt larger than at the tip. Among va- 
rieties with high knob numbers the majority are almost 
cylindrical in shape. There is reason to expect such an 
association for in hybrids of maize and teosinte many of 
the segregates are more nearly cylindrical than the maize 
[ 226 ] 
