of Tripsacum which enabled the new plant to survive in 
the wild. 
As a result of this hybridization there also arose new 
varieties of maize with varying numbers of 'Tripsacum 
knobs. The knobs themselves, comprising only hetero- 
chromatin, had no genic effects, but associated with the 
knobs were usually small segments of ‘Tripsacum chro- 
matin homologous or partially homologous to those in 
maize. This admixture with Tripsacum chromatin pro- 
duced profound modifications in the maize. New varieties 
‘ame into existence in which the seeds were smaller, more 
inclined to be indented, more uniform in size and shape 
and arranged in straight rows on the rachis. The cobs 
became firmer and less susceptible to shattering, the 
stalks became tough and resistant to lodging, the leaf- 
sheaths became glabrous instead of pubescent and the 
plants became resistant to smut. These new ‘Tripsacoid 
varieties were much superior to the pure maize at lower 
altitudes, and rapidly replaced it, if indeed it was ever 
extensively grown there. At high altitudes, however, at 
6500 feet and more, the original maize succeeded in hold- 
ing its own and became but slightly contaminated with 
Tripsacum. In the meantime derivatives of the Tripsa- 
cum contaminated maize spread to all parts of Central, 
North and South America where maize is grown, except 
to the Andean region of Peru, Bolivia and Ecuador where 
pure maize (some of it quite similar in characteristics to 
the type introduced into Central America) continued, as 
it has in Central America, to resist the encroachment of 
the new varieties. 
This imaginary picture accounts for all of the essential 
tillate inflorescences) are inherited as simple Mendelian characters. 
Unpublished studies by the senior author show the inheritance to be 
less simple than this when Florida teosinte rather than Durango is 
one of the parents, but even here the situation is probably not unduly 
complex. 
[ 238 ] 
