May 16, 1921 
Heritable Variations in Cotton 
231 
and as compared with the selfed line they were higher in 8 and lower in 3 
characters. If we regard as significant only such differences as amount to 
at least three times the probable error, the parent progeny was significantly 
more variable than the bulk stock in 4 and significantly less variable in 1 
of the 12 characters. As compared with the selfed population, the 
parent progeny was significantly more variable in 3 and significantly less 
variable in none of the characters. 
The high degree of homozygosity apparently attained by the commer¬ 
cial stock as a result of simple selection without controlled selfing is indi¬ 
cated by the fact that five generations of controlled selfing has rendered 
the “selfed” line significantly less variable than the “bulk” stock in only 
2 of the 12 characters, while in 1 character it is significantly more variable. 
No significant difference in variability is shown in respect to the 9 remain¬ 
ing characters. 
FIBER AND SEED CHARACTERS OF THE PARENT PROGENY AND OF 
THE PRESENT COMMERCIAL STOCK 
Especial interest attaches to the characters fiber length, lint index, and 
seed fuzziness because of their practical importance and because since the 
commencement of the breeding work with the Pima variety attention has 
been focused upon increasing the length and abundance of the fiber and 
obtaining a high degree of uniformity in these characters. An indication 
of what has been accomplished along these lines is afforded by the fre¬ 
quency distributions in Table II. The maximum and minimum length 
of fiber, abundance of fiber, and fuzziness of seeds of the parent progeny 
and of a corresponding number of plants of the commercial stock are 
represented in Plates 50, 51, and 52. 
Length of Fiber. —It is evident from the data in Tables I and II 
that the immediate progeny of the parent plant of the. Pima variety 
was much more variable in length of fiber and had a significantly lower 
mean for this character than a random sample of the present commercial 
stock of strain 5-3. This strain, as indicated in the pedigree shown in 
figure 1, was derived from a granddaughter of the original Pima plant, 
selected in 1912 largely on the basis of its superior length of fiber. The 
difference between the means of the “parent” progeny and of the bulk 
stock was 3.8 mm., hence more than inch, and the difference was 17 
times greater than its probable error. The selfed line of strain 5-3 was 
almost intermediate in length of fiber between the “parent progeny” 
and the “bulk,” its mean differing from those of the other two popula¬ 
tions by amounts equivalent to 9 and 10 times the probable error of the 
differences. The ancestors of this closely inbred line, beginning with 
plant Pi in 1914, had not been selected with reference to this character 
and would seem to have represented very nearly the minimum potenti¬ 
ality of strain 5-3 in respect to length of fiber. The coefficients of 
variation of the bulk and selfed populations do not differ significantly, 
but both were significantly less variable than the parent progeny. 
