May 16, 1921 
Heritable Variations in Cotton 
241 
coefficient of correlation having been o.oi±o.o5. The means of 22 
progenies of the third generation of this hybrid, grown in 1920, showed 
a positive rather than a negative but not a significant correlation, the 
coefficient having been 0.22 ±0.14. The absence of a significant and 
negative correlation between these characters in the second and third 
generations of a known hybrid between Egyptian and Upland cottons 
would be evidence, if evidence were needed, that the association of a 
high percentage of 4-lock bolls with great reduction of the petal spot 
in these Pima lines is not attributable to recent hybridization with Up¬ 
land cotton. 
SUMMARY 
Evidence is presented in this paper of the occurrence of heritable 
variations in the Pima variety of American Egyptian cotton, which is 
probably the most uniform variety of cotton now grown on an ex¬ 
tensive scale. 
Comparison of a progeny grown from seed of the parent individual of 
the variety with the present commercial stock proves that there has 
been significant improvement in the length and abundance of the fiber, 
as well as in the uniformity of these characters. This is shown by com¬ 
parison of the means and coefficients of variation (Table I) and of the 
frequency distributions (Table II). 
Indications of the occurrence of heritable variations have been ob¬ 
tained in roguing fields of the Pima variety, although the variations 
are much less numerous and are of much smaller magnitude than those 
which were observed in fields of the older Yuma variety. 
The records of the breeding work with Pima cotton supply addi¬ 
tional evidence of the occurrence of slight, heritable variations, 
none of which could be considered as outside the normal range of varia¬ 
tion of this variety. They indicate, however, that something may be 
accomplished by selection in regard to characters of practical importance. 
A much more striking variation, characterized by the complete or 
nearly complete absence of the dark red spot near the base of the petal, 
associated with an increased percentage of 4-lock bolls, was found to be 
heritable in a high degree. The nature of this variation and the cir¬ 
cumstances of its occurrence suggest the possibility that Upland cotton 
(Gossypium hirsutum) or Hindi cotton (G. punctatum Sch. and Thon. ?) 
may have been involved in the remote ancestry of the Pima variety. 
The fact that heritable variations are found in this apparently uni¬ 
form variety is thought to justify the continuance of selection and line 
breeding and the roguing of seed increase fields. 
