5°8 
Journal of Agricultural Research 
Vol. XXVII, No. 7 
The means for the dominant plants showed no difference between the 
earlier and the later flowers but, for the recessive plants, the mean for 
the earlier flowers was 0.24±.039 grade higher than the mean for the 
later flowers. A similar comparison in 1923 on 285 dominant and 267 
recessive plants on which 10 flowers per plant had been graded showed, 
in both groups, a difference of o. 1 grade in favor of the earlier flowers, the 
difference in one case having been 6 and in the other case 4^ times its 
probable error. In both years, therefore, comparison of the earlier with 
the later flowers on the same plants gave evidence of a mathematically 
significant but practically unimportant difference in grade of petal spot 
in favor of the earlier flowers. 
The fact that the early, as compared with the later flowers produced 
by the same individual, tend to give a slightly higher average grade of 
petal spot seems at first glance inconsistent with the fact previously 
noted (p. 502) that the petal spot is apt to be better developed on retarded 
plants than on plants which have grown more rapidly. The apparent 
contradiction disappears if we consider that the earlier flowers on the 
more advanced plants were produced when these plants were in a stage 
of growth more nearly comparable to that of the retarded plants. 
A more marked reduction in the petal spot takes place towards the 
end of the flowering season. On October 6, 1923, it was noted that in 
both the dominant and recessive populations the flowers showed a pro¬ 
nounced diminution in the size and intensity of the spot as compared 
with the condition on August 18, when the grading ended. 
FREQUENCY OF 4-LOCK BOLLS IN RELATION TO PETAL SPOT 
Observation of the growing plants and measurement of the leaves, 
bolls and fiber have shown that the families which furnished the spotless 
parents of the hybrids here described are typical Pima except in the 
development of the petal spot and the proportion of 4-lock bolls. In 
other color characters of the flowers, greenish yellow color of the petals 
and empire yellow color of the pollen, they show no departure from the 
type. In percentage of 4-lock bolls, the descendants of both of the spot¬ 
less selections of 1917 exceed the average for the variety as grown at 
Sacaton. This was shown by data from the progenies grown in 1919 
and 1920, in comparison with the general stock of Pima cotton. 11 Ad¬ 
ditional evidence was obtained in 1921 and 1922, by comparing the spot¬ 
less parental progenies with progenies representing the normal or spotted 
parents of the hybrids. Data for both the parental and the hybrid popu¬ 
lations are given in Table XV. 
It is clear from the data in Table XV that in 1921 and 1922 the prog¬ 
enies representing the two spotless families had significantly higher 
mean percentages of 4-lock bolls than the progenies descended from the 
spotted parents of the crosses, just as, in 1919 and 1920, the spotless 
families had significantly higher percentages than the “bulk” Pima with 
which they were compared. It is also evident that the descendants of 
spotless plant No. 3 continue to give very significantly higher means for 
this character than the descendants of spotless plant No. 1. In Fj the 
percentage of 4-lock bolls in one of the crosses resembles that of the 
progeny representing its spotless parent, while the other cross gave an 
almost intermediate percentage. In F 2 , the mean percentage of 4-lock 
11 Kearney, Thomas H. HERITABLE variations in an apparently uniform variety OF COTTON. 
In Jour. Agr. Research, v. 21, p. 237-241. 1921. 
