22 
BULLETIN 1164, U. S. DEPARTMENT OE AGRICULTURE. 
expected if total absence of petal spot is a simple, recessive Mende- 
lian character, as given in Table 4, show that the difference between 
the actual and the expected percentage of plants having no petal 
spot was only twice its probable error. 
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Fig. 27.— Petal spot: Frequency distribution of 
Holdon X Pima Fs cotton plants, by grades, 
as used in computing the correlations. The 
ordinate figures indicate the number of plants 
as a percentage of the total population. 
Fig. 28. — Stamen length: Frequency distribution 
of Holdon X Pima F? cotton plants, by grades, 
as used in computing the correlations." The or- 
dinate figures indicate the number of plants as 
a percentage of the total population. 
Table 4. — Numbers and percentages of the F 2 population of 215 individuals of Holdon- 
Pima cotton hybrids, showing the presence, in varying degrees, and the absence of petal 
spot and (he numbers eind percentages to be expected on the basis of a monohybrid 
fiio. 
State of petal spot. 
Petal spot present. 
Petal spot absent . 
Number. 
Actual. Expected. 
1 52 
161 
54 
Percentage. 
Actual. Expected. 
70.7 
29.3±2.09 
75.0 
25.0 
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Fig. 29.— Anther color: Frequency distribution 
of Holdon X Pima F 2 cotton plants, by grades, 
as used in computing the correlations. The 
ordinate figures indicate the number of plants 
as a percentage of the total population. 
Fig. 30.— Pistil length: Frequency distribution 
of Holdon X Pima F 2 cotton plants, by grades, 
as used in computing the correlations. The or- 
dinate figures indicate the number of plants as 
a percentage of the total population. 
The mean grade for petal spot of the F x progeny of 24 plants grown 
in 1920 was 4.2, as compared with mean parental grades of in 
Holdon and 6.5 in Pima and a mean grade of 3.6 for the 152 F 2 
individuals in which the spot was present. This character showed 
considerable variation in F x , as is indicated by the frequency distri- 
bution in Table 5. 
