54 
Research Bulletin No. 2 
INHERITANCE OF DIAMETER OF EARS. 
Diameter of ear is directly correlated with number of rows 
and with seed size and probably also, negatively, with length of 
ear. In general, ears show less fluctuation in diameter than they 
do in length. 
Table 18 exhibits the data obtained from the cross of Oali 
fornia pop and Missouri dent. As grown in 1911, the former. 
Nos. 834 and 839, had a mean ear diameter of a little less than 
25 millimeters and the latter. No. 833. a mean diameter of a 
little over 50 millimeters. The mean diameter of ¥ 1 ears grown 
the same year. Nos. 836 and 837. was nearly 42 millimeters, or 
about 4 millimeters greater than the mid-parental value. Tt 
seems likely that this small increase over the mid-parental di- 
ameter is due to the increased vigor accompanying heterozygosis, 
for the mean diameters of the F 2 families averaged only a little 
over 37 millimeters, or almost exactly half way between the 
parents. The F 1 families grown under the more favorable con- 
ditions of 1910, Xos. 502 and 503, naturally had somewhat 
greater ear diameters than the F, families of 1911. 
The ranges of variation of the F 2 families were not great, 
having extended only from a little above the mean of California 
pop to a little below the mean of Missouri dent. While the 
number of individuals of no one F 2 family was large, the total 
number of individuals of the six F 2 families was 321. or more 
than a sufficient number to give an even chance of obtaining all 
possible combinations of factors if the parents differed by only 
four factors. It is probable, however, that neither the seed size 
nor the number of rows of the parents differed by so few as two 
factors and, since diameter of ears is directly related to both of 
these other ear characters, it would not be strange if the differ- 
ence in diameter of ears between Missouri dent and California 
pop were due to as many as seven or eight factors. In the latter 
case, something like 65,000 F 2 individuals would have to be grown 
to afford an even chance of obtaining a single plant each, 
gametically like the two parent types as regards factors in- 
fluencing diameter of ears. In this case, some of the smallest 
and some of the largest F 2 ears of the 321 should prove hetero- 
zygous for diameter factors and should, therefore, produce F 3 
plants more extreme than any plants of F 2 . 
This apparently is exactly what happened in case of the 
cross of Missouri dent with Tom Thumb pop. the data for which 
are presented in Table 19. Several of the F 3 families contained 
individuals with ears of smaller diameter than any F 2 ear. In 
fact the mean diameter of Xo. 1132 was practically equal to the 
diameter of the smallest ears of the F = families grown the same 
