ognized the relationship and mentioned it several times. 
Weatherwax (51) stated without reservation: ‘‘The 
average number of knobs in maize varieties decreases 
with the distance north or south from Central America 
—that is, with distance from the area where contamina- 
tion with teosinte is most likely to occur.’’ So far as we 
are aware, Randolph is the only student of this problem 
who denies the existence of a real correlation between 
the number of knobs and proximity to the general re- 
gion of Guatemala. 
High knob number has been studied in relation to yield 
(50, 54) and other plant characters, but this topic will be 
reviewed in a separate publication (27). 
We have never interpreted these correlations as 
‘‘proof’’ (32) of recent admixtures of corn and Tripsa- 
cum. They are best explained, however, on the assump- 
tion that corn not only is older than teosinte but that it 
was widespread over the hemisphere before teosinte orig- 
inated in Guatemala. According to this assumption, the 
knob-bearing chromatin of teosinte diffused through 
corn in all directions, by hybridization, but the greatest 
concentration continues to be in the vicinity where teo- 
sinte originated and still occurs. 
CHROMOSOME CHARACTERS OF CorN 
AND ITs RELATIVES 
A great body of literature pertaining to the chromo- 
somes of corn, teosinte and Tripsacum is in existence. 
Except for the significance of the number and position 
of knobs, this topic is relatively free from controversy, 
and the pertinent facts may be stated briefly. 
The normal diploid chromosome number of corn is 20, 
and no stable aberrant numbers are known, although 
some varieties have supernumerary chromosomes (B- 
chromosomes) which behave irregularly during meiosis 
[ 867 | 
