of Central and North American varieties are contami- 
nated with Tripsacum. It becomes necessary therefore to 
attack separately the numerous problems which are sug- 
gested by each of the three more or less independent parts 
of the hypothesis. This paper concerns itself only with 
the third. How extensive has been the introgression of 
Tripsacum into maize to produce new types and where 
is the region—the secondary center of origin of cultivated 
maize varieties—in which this phenomenon has occurred / 
In approaching this problem the conclusions of Man- 
gelsdorf and Reeves are utilized as the working hypothe- 
sis and the results obtained are discussed in terms of that 
hypothesis. Other interpretations can be made, however, 
and are discussed later. 
In the previous publication it was pointed out that 
in the number and position of chromosome knobs, teo- 
sinte, as it isin many other characteristics, is intermediate 
between North American maize and Tripsacum.’ This 
fact suggested that pure maize, uncontaminated by Trip- 
sacum, might possess knobless chromosomes. Such varie- 
ties were sought and found in the Andean region of Peru, 
Bolivia and Ecuador. It was also found that these vari- 
eties differ from the majority of those of North and Cen- 
tral America in lacking characteristics which might have 
been derived from Tripsacum. The Andean varieties are, 
to use a term proposed by Anderson and Erickson (1), 
much less ‘‘'Tripsacoid’’ than the predominating maize 
of Central or North America. 
Another corollary of this same line of reasoning is 
? Chromosome knobs are deeply-staining pycnotic enlargements visi- 
ble at high magnifications when the chromosomes are in the pachytene 
stage. They have been observed only in the three American Maydeae: 
Tripsacum, Euchlaena and Zea. In Tripsacum and Guatemalan teo- 
sinte they are numerous and are confined to the ends of the chromo- 
somes. In maize and Mexican teosintes their number is variable and 
their position frequently subterminal. 
[ 218 | 
