CHARACTERS IX AN UPLAND-EGYPTIAN COTTON HYBRID. 
15 
Another expression of the comparative variability of the parental 
and hybrid progenies was obtained by averaging, for each population, 
the coefficients of variation of the measured characters and the 
standard deviations of the graded characters, the averages being 
given in Table 3. 
Table 3. — Averages of the coefficients of variation end of the standard deviations of the 
parental and hybrid 'populations of Hoi don and Pima cotton. 
Average of the — 
Parental. 
Hybrid. 
Holdon. 
Pima. 
Fi. 
F 2 . 
Coefficients of variation of the 28 measured charac- 
ters 
19.66±2.17 
.22- .05 
10.62^0.96 
.29± .07 
8.31±0.7S ' 26.924-2. n4 
Standard deviations of the 11 graded characters 
.38± .08 
1.37± .08 
Comparing the averages of the coefficients of variation for the 
measured characters, Holdon is found to be considerably the more 
variable of the parental populations, and the difference between the 
average variabilities of the Holdon and Pima populations amounts 
to nearly four times the probable error of the difference. F 1 is much 
less variable than the Holdon parental population, and the difference 
amounts to about five times its probable error. The average varia- 
bilities of Fj and the Pima parental population do not differ signifi- 
cantly. The average variability of F 2 is very significantly greater 
than that of ¥ x and of the less variable parental population (Pima), 
but F 2 was not significantly more variable than the Holdon parental 
population, the difference in average variability amounting, in this 
case, to only about twice the probable error of the difference. 
Comparison of the averages of the standard deviations for the 
graded characters shows no significant differences in variability among 
the two parental and the F l populations, while F 2 is greatly and sig- 
nificantly more variable than the other three populations. 
Comparison of the average of the coefficients of variation for 
measured characters of F l with that of F 2 shows F 2 to be more than 
three times as variable as E r A similar comparison on the basis 
of the standard deviation for the graded characters shows F 2 to be 
three and one-half times as variable as F x . 
These data, however, give a very inadequate expression of the 
relative variability of the second generation of this hybrid, for, in ad- 
dition to the characters here considered, many appeared in F. : which 
were not expressed or but slightly expressed in either parental popu- 
lation. (See pages 39 to 41.) If these extraparental characters are 
taken into account, it must be concluded that the diversity in F 2 was 
vastly greater than in either parental population or in the first 
generation of the hybrid. 
FREQUENCY DISTRIBUTIONS OF THE SECOND GENERATION OF 
THE HYBRID. 
The frequency distributions for the 39 characters of the hybrid F 2 
population grown in 1919 are shown in Figures 3 to 41. The num- 
bers on the axis of ordinates represent percentages of the total 
