Feb. i6,1924 
Inheritance of Petal Spot in Pima Cotton 
.501 
Table IX .—Segregation in as indicated by comparison of the means of the spotted 
and the spotless plants in the F 2 progenies and of the means of the dominant and recessive 
F 3 populations descended from each F x plant 
Fi pa¬ 
rent and 
Fj prog¬ 
eny No. 
Grade of 
Means of the a 
i classes in Fa. 
Means of the F3 populations. 6 
Fi progeny. 
the Fi 
parent. 
Spotted 
plants.® 
Spotless 
plants. 
Dominant. 
Recessive. 
1-3-12-14X12. 
20 
7.0 
i ~ 
6. 7i±o. 076 
O. 44 ±0. 050 
7 - 79 ±°- ° 3 I 
I. o6rbo. 037 
1-3-12-14X14. 
! 28 
7.6 
|6. 961b . 071 
. 70± • 062 
7. 89^ • 028 
1. 78 ± .045 
Differences... 
j 
.6 
.25± . 104 
. 26± . 080 
. iodz . 042 
.72 rb . 058 
3-2-4-1X13. 
21 
7. 2; 
6. 90^ . 101 
• 64 dt . 131 
8. 06dr . 026 
I. 42 dz .054 
3-2-41X13. 
Differences... 
24 
7 - 9 ! 
• 7 
I7. 11 ± . 092 
. 2lrt . 136 
. 68± . 078 
. 04 dz • 152 
8. 23 dz • 027 
. i 7 ± • °37 
1 
l.98db .055 
. 56 dz .077 
® Dominant and heterozygous plants. b Each Fa population comprises two progenies, taken as one array 
EVIDENCE OF MODIFYING FACTORS 
The questions suggest themselves whether, in addition to the major 
factor determining full development of the spot as contrasted with its 
almost complete absence, there are minor factors which modify the 
degree of its expression; and whether such factors have been variously 
recombined in the hybrids. 
No evidence of modifying factors is afforded by the results of selection 
during successive generations in the parental populations. In 1920, 
1921, and 1922 the plant which gave the lowest average grade for petal 
spot in each of the recessive parental progenies was selfed and became 
the progenitor of a progeny grown the following year. Comparison of 
the parental values and the progeny means, as given in Table X, does 
not show a tendency to reduction of the spot. It will be shown presently 
that the apparent marked increase in the progenies grown in 1923 is 
probably attributable to the lateness of flowering of most of the plants 
in the parental progenies of that year. 
In 1922 two plants were selfed in each of the parental progenies, these 
plants having represented the extremes of development of the spot 
for the population in question. Progenies of each of these plants were 
grown in 1923. The progeny means, as stated in Table XI, showed no 
differences of probable significance except in the third pair and in that 
case the.higher mean was yielded by the progeny of the plant which 
had given the lower value. 
Tabes X .—Grade of petal spot of selections in the recessive parental populations and 
mean grade of the progenies of these selections 
Selection and year. 
Grade of the 
selected 
individual. 
Mean grade 
of its prog¬ 
eny grown 
the year 
following. 
1-3-12, No. 14 (1920)...! 
1 0 
1. 2±o. II 
1-3-12-14, No. 2 (1921).I 
O. 7 
• 7± .04 
1-3-12-14-2, No. 25 (1922). 
•4 
2. 3± .09 
3-2-4, No. 1 (1920)..| 
O 
. 7± • 06 
3-2-4-1, No. 22 (1921).| 
. 2 
. 7 ± *03 
3-2-4-1-22, No. 27 (1922). i 
. 2 
1. 8± .07 
74026—24 -6 
