Feb. 16,1924 
Inheritance of Petal Spot in Pima Cotton 
499 
The spotted portion (grades 5.5 to 9) of the frequency distributions of 
the heterozygous F 3 ’s (Table VI) is bimodal in 7 of the 8 progenies, 
indicating that the heterozygotes are partly distinguishable from the 
dominants. Further evidence that such is the case is afforded by the 
fact that all of the 8 F 2 plants selected in 1922 as nearest intermediate 
(grade 5.3 to 6.2) gave F 3 progenies which segregated. While, for reasons 
stated in discussing the similar condition in F 2 , the heterozygotes giving 
relatively high grades can not be distinguished with certainty from the 
dominants giving relatively low grades, it may be worth while to note 
that in the spotted portion of the whole F 3 population there were 163 
plants having an average grade not higher than 7 and 86 plants having 
an average grade higher than 7, a ratio of 1.9 :i. While this classification 
is admittedly arbitrary, it indicates that the phenotypic ratio is 1 .2 :i. 6 
The statistical constants, as computed from the frequency distributions, 
of the parental and the homozygous F 3 progenies are stated in Table VIII. 
Comparing the means for groups of progenies having a common origin 
taken as one array (heavy-faced figures in Table VIII),it will be noted 
that the populations derived from the two dominant parents (12 and 13) 
of the original hybrids do not differ significantly, and that this is likewise 
true with respect to the populations representing the two recessive parents 
(1-3-12-14 and 3-2-4-1). Data given in Table IV show that in the pre¬ 
ceding generation also the populations representing, respectively, the 
dominant and the recessive parents of the hybrids did not differ sig¬ 
nificantly in their means for petal spot. On the other hand, the popu¬ 
lation embracing the four dominant F 3 progenies derived from the cross 
1-3-12-14X 12 differs slightly, but significantly, in its means from that 
of the combined population of dominant F 3 *s derived from the cross 
3-2-4-1X 13, the difference having been 0.30 ± 0.028. Similarly, the mean 
for the combined recessive F 3 progenies derived from the cross 1-3-12- 
14 X 12 shows a small but probably significant difference from that of the 
combined recessive F 3 progenies derived from the cross 3-2-4-1X 13, the 
difference having been 0.21 ±0.055. In both cases it is the descendants 
of the cross 3-2-4-1X 13 which gave the high mean. 
There are also significant differences among the several F 3 progenies 
derived from the same original cross and even between progenies which 
had had the same Fj grandparent. Of the two dominant F 3 progenies 
descended from (1-3-12-14X 12) F t plant No. 20, progeny 20-14 gave a 
significantly lower mean than progeny 20-15 (difference 0.4 ±0.067). 
Of the two dominant F 3 progenies descended from (3-2-4-1 X13) F, 
plant No. 24, progeny 24-18 gave a significantly lower mean than prog¬ 
eny 24-46 (difference 0.3 ±0.050). Of the two recessive F 3 progenies 
descended from (1-3-12-14X 12) Fj plant No. 28, progeny 28-32 gave a 
significantly higher mean than progeny 28-49 (difference 0.5 ±0.086). 
Of the two recessive F, progenies descended from (3-2-4-1 X13) F, 
plant No. 21, progeny 21-16 gave a significantly higher mean than prog¬ 
eny 21—22 (difference 1.2 ±0.072). Thus significant differences are 
found among the dominant or recessive descendants of each of the four 
F x individuals which gave rise to the F 2 ’s grown in 1922 and the F 3 ’s 
grown in 1923. 
6 On this basis of classification in the spotted group, the whole segregating F3 population (8 progenies as 
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