May 16, 1921 
Heritable Variations in Cotton 
235 
and progenies were grown in 1919 from the resulting selfed seed. One 
of these progenies resembled the parent individual in having the surface 
of the boll more deeply pitted than in typical Pima. Another progeny 
showed a tendency to produce shorter and plumper bolls than the Pima 
type, while a third progeny showed the “bull-stalk” habit as well as a 
tendency to produce short, plump bolls. So far as this evidence goes it 
indicates the inheritance of slight variations in the Pima variety. 
The recognition of these various types is always easiest in a well- 
grown field of cotton. If the plants are either too rank or too stunted, 
the variations are more or less masked. Certain soil conditions appear 
to favor the expression of a certain type. Thus, fields have been ex¬ 
amined where the growth was subnormal and where all the plants showed 
a tendency to the stiff, grayish form which in most fields occurs scatter- 
ingly among plants of normal habit and color. O11 the other hand, 
where the growth is very rank, the “bull-stalk” type can scarcely be 
recognized. 
EVIDENCE OF THE OCCURRENCE OF HERITABLE VARIATIONS 
OBTAINED IN LINE BREEDING 
The records of the breeding work (selection) which has been carried 
on with the Pima variety since its origin in 1910 have been scanned for 
evidence of the occurrence of heritable variations. Unfortunately the 
stem, leaf, and boll characters had not been recorded systematically, but 
a few data based upon careful measurements are available. The type of 
plant which has been kept in mind as the ideal in breeding work with the 
Pima variety is shown in Plate 53. It is characterized by the absence 
of vegetative branches and by the development of good fruiting branches 
from near the base to the summit of the axis. The relationship of the 
various strains and progenies mentioned in the following pages is shown 
in figure 1. 
In 1914 two groups (5-3 and 5-13), descended from sister plants in 
progeny No. 5 of 1912, were compared with respect to certain stem and 
branch characters and showed significant differences, as given in Table 
III. 
Table III .—Means for stem and branch characters in two lines of the Pima variety grown 
in IQ 14 
Character. 
Group 5-3 
(24 plants). 
Group 5-13 
(26 plants). 
Differences 
between means. 
Axis length (cm.). 
178. o± 1. ss 
40. 5 ± -34 
44 - °± • 33 
102. 3± 10. 76 
194- 5 ± 2 - 11 
42- 8± . 43 
45 - 5 ± • 25 
172. 4±i2. 88 
16. 5± 2. 62 
2 - 3 ± -55 
i- 5 ± • 41 
70. i±i 6 . 80 
Axis intemode number. 
Axis intemode length (cm.) 1 . 
Limb index 2 . 
1 Value for each plant obtained by dividing the length of the axis by the number of intemodes. 
2 Aggregate length of vegetative branches divided by length of axis. 
