Feb. 16, 1924 
Inheritance oj Petal Spot in Pima Cotton 505 
Table XIII .—Overlapping of the dominant and recessive populations of IQ23 in grade 
of petal spot of the individual flowers 
Group. 
Total 
number of 
flowers 
graded. 
Numbers of flowers 
grading. 
4.0 
4-5 
5-o 
Dominants.* 
3,843 
3, 7oo 
9 
97 
7 
15 
I 
Recessives.i 
\J 
5 
i 
The average degree of variation on the individual plant may be shown 
by computing, for a given population, the mean of the differences be¬ 
tween the flower graded highest and the flower graded lowest on each 
individual. In computing these means, plants were disregarded on which 
fewer than ten flowers were graded. The means were computed sepa¬ 
rately for the dominant and for the recessive parental and F 3 populations, 
each as one array, and for the dominant, heterozygous and recessive 
plants in the segregating F 3 progenies, * * * 7 giving, in all, 5 populations of 
which the mean and maximum variation, on the individual plant, are 
stated in Table XIV. 
Table XIV .—Mean and maximum variation of petal spot grade on the individual 
plants in the dominant and recessive parental and F 3 populations and in the dominant, 
heterozygous and recessive classes of the segregating F 3 progenies. 
I Range of grades on the 
i individual. 
Population. 
Num¬ 
ber 
of 
plants. 
j 
Mean. 
Maximum 
and (in 
parenthesis) 
the number 
of plants 
showing it. 
Dominant parental and F 3 ... 
297 
278 
62 i 
2. I0±0. 035 
2. 64 ± . 026 
2. i8± . 060 
5 - 0 (6) 
5 -0(1) 
4 - S (2) 
5- 0 (3) 
4.0 (a) 
Recessive parental and F 3 . 
Dominants in segregating F 3 *s. 
Heterozygotes in segregating F 3 ’s. 
i 
107 i 
66 | 
2. 55 ± -057 
2. 42 ± -057 
Recessives in segregating F 3 ’s... 
It is noteworthy that variation amounting to four or five grades is 
shown by a few individuals in each population. Comparison of the mean 
ranges shows significantly less variation in the dominant than in the 
recessive population. The dominants in the segregating F 3 progenies 
also are individually less variable than the heterozygotes and the re- 
cessives, although the difference between dominants and recessives is, 
in this case, slightly less than three times its probable error. The smaller 
variation of the dominants may be apparent rather than real, for the 
reason that slight differences are less easily detected when the spot is 
strongly developed than when it is weakly developed. 
1 Plants giving an average grade of 7.3 or higher were taken as dominant, 7.3 having betfn the lowest 
average given by any plant in the dominant parental populations. Plants giving an average grade lower 
than 7 and higher than 5 were taken as heterozygotes, the comparatively few individuals which averaged 
7 to 7.3 having been left out of account as of uncertain classification. It is believed that classification on 
this basis is sufficiently accurate for the purpose in view. There could be no question as to the identity 
of the recessives. 
