but also in certain internal morphological features of the 
chromosomes. 
Varieties with still higher knob numbers, numbers up 
to sixteen, were found in other parts of Guatemala. No 
particular significance attaches to this, however, for the 
sampling errors are large and it is reasonable to assume 
that plants with as many as sixteen or more knobs would 
be discovered in this area if an exhaustive search were 
made. This is especially probable since some of the most 
Tripsacoid varieties from this area, being very late in 
maturity, were not examined cytologically. Of the twen- 
ty-one varieties planted from the four localities in Hue- 
huetenango with highest knob numbers, only eleven were 
early enough for cytological examination. 
Knob number is only one of the characteristics by 
which the degree of contamination with Tripsacum can 
be measured. It is perhaps one of the most useful because 
it is a precise quantitative datum. We assume that the 
chromosome knobs of present-day corn were derived from 
Tripsacum through teosinte and on that assumption the 
number of knobs becomes a rough measure of the amount 
of 'Tripsacum admixture. It is desirable, however, to test 
this assumption by determining whether knob number is 
associated with other characteristics which might have 
been derived from Tripsacum. 
That there is such a relationship can be immediately 
discerned even without studying other characteristics in 
detail. When ears of these varieties were received from 
Dr. McBryde it was at once apparent that some of them 
resembled quite closely certain varieties from the Andean 
region. These were tentatively designated as ‘‘Andean”’ 
types. The average knob number of this group, compris- 
ing sixteen varieties, is 4.7, only slightly more than half 
the average number 7.9 for the population as a whole. 
In other words it was possible on the basis of the general 
[ 223 ] 
