May 16, 1921 
Heritable Variations in Cotton 
239 
INHERITANCE OF SPOTLESS OR FAINTLY SPOTTED PETALS 
The variations which have been considered thus far are so slight that 
in the absence of evidence of their heritability, they would be regarded 
as mere fluctuations. Especial interest attaches to a variation which is 
outside the normal range of variation not only of the Pima variety but 
of the Egyptian type of cotton. 
Inspection of the 4-lock progenies in 1919 revealed the surprising 
fact that in all plants in these three progenies there was either total 
absence or very faint development of the dark red spot near the base of 
the petal which is so marked a characteristic of the Pima variety and of 
Egyptian cotton in general. In this respect the 4-lock plants contrasted 
strikingly with all other Pima progenies in the same field as well as with 
the bulk stock of this variety grown in adjacent fields. Although there 
is appreciable variation in the size and in the intensity of color of the 
petal spot in Pima cotton, no such approach to complete absence of the 
spot had been observed hitherto except in plants which were obviously 
hybrids with Upland cotton. 
The 38 plants of the three 4-lock progenies in 1919 were graded by 
Mr. W. G. Wells with respect to degree of development of the petal spot, 
grade 8 indicating the extreme development in typical Pima cotton and 
grade o indicating complete absence of the spot, as is the case in most 
varieties of American Upland cotton (Gossypium hirsutum L.). Two or 
three flowers were separately graded on each plant, and the averages of 
the resulting grade numbers were used in computing the mean for the 
entire population, which was i±o.o4 as compared with a mean of 
7.5 ±0.19 for a Pima population of 13 plants which had normally de¬ 
veloped petal spots. Of a total of 106 flowers examined, in the 4-lock 
progenies, 16 on 14 different plants showed no trace of a petal spot, and 
none of the flowers was graded higher than 2. 
Four progenies, descended from two of the individuals which were 
selected in 1917 1 for a high percentage of 4-lock bolls, were grown in 
1920. Ten flowers on each plant in these four progenies were graded 
by the writer with respect to the degree of development of the petal spot, 
and the progeny means were computed from the mean grade of the 10 
flowers per plant. The results are stated in Table IX. 
Table IX .—Mean grade of petal spot development in the 4-lock progenies of IQ20 
Progeny. 
Num¬ 
ber of 
plants. 
Number of 
flowers. 
Mean grade of 
petal spot. 
T C 
T CO 
1 . o±o. 06 
I. o± . 04 
n -4- 0 a 
O . 
1 — 7—12 . 
A 0 
A c 
A CO 
7—2—A . 
38 
A 0 
40 w 
380 
AOCl 
O * . . . 
7-2- < . 
. yn: • 
•9± • °3 
1 It is a remarkable coincidence that of two individuals which were selected as having a high percentage 
of 4-lock bolls, although at the time of selection this peculiar character of the flowers was not noted, the 
descendants have shown themselves to be alike in the subnormal development of the petal spot. Asitis 
unlikely that this character would have been overlooked if it had been common to all plants of the strain 
in which these selections were made in 1917, the most probable explanation of the coincidence is that the 
two individuals in question were sisters. 
