A. TYPES OF BOOTING.

The races of booted poultry used have been as follows: First, bantam Cochins of two varieties; second, a bantam Dark Brahma; and third, the Silkie. In my representatives of the first two groups, but particularly in the Dark Brahma, the amount of booting is variable. In one type the outer third of the shank in the newly hatched chick is covered by strong, heavy, specialized feathers, directed outward, while the middle and inner thirds are covered by smaller, finer, imbricating feathers sparsely placed and resembling reduced contour-feathers. In most individuals the transition from the one kind to the other is gradual, while in others it is sharp, and in a few the outer third only of the shank is feathered. In the Silkies, which the standard poultry books describe as being more sparsely feathered on the shank,[8] the outer zone of feathers is the only one developed; and, occasionally, as table 31 shows, even these feathers may be lacking. We have thus two types to distinguish—the extended (Cochin, Brahma) type and the restricted type.

B. NORMAL VARIABILITY.

To appreciate the results of hybridizing we must first examine the variability of pure-blooded races. This is done in table 31.

Table 31.—Distribution of boot-grades in the offspring of Cochin, Dark Brahma, and Silkie parents.

[A] Determination made on embryo chicks.
A. OFFSPRING OF COCHIN PARENTS.
Pen No.Mother.Father.Grades of boot in offspring.
No.Boot-
grade.		No.Boot-
grade.		012345678910Average.
84822971054510.........1......1......1189.43
77625741027328........................3269.27
8482300854510........................1259.25
7762570627328..................11...1118.71
8482075954510...............11.........48.50
7762072627328..................1...4228.44
758130654510...............11139...8.20
7762073627328.............12...221018.00
7762300627328............1...136528.00
7581311054510...............1...46117.96
7762297627328.........1...1...36627.95
7761132327328.........1111368...7.57
7762937727328..................1331...7.50
7762299727328......1......1147317.44
Totals (199)......13389244761438.24
B. OFFSPRING OF DARK BRAHMA PARENTS.
[All individuals have sprung from No. 121 ♀ (boot of grade 9) and No. 122 ♂ (boot of grade 6).]
816203061226...........................139.8
703203061226..................420368.3
81612161226...............1312458.3
816597961226..................102......7.3
816235351226............[A]11101027.1
816583551226.........[A]1012......136.5
816584051226.........[A]1......1.........16.3
703235351226............113...1......5.8
Totals (61) .........22415369207.62
C. OFFSPRING OF SILKIE PARENTS.
73446847743......12......11.........4.20
734100237743......14...13............4.11
734841(?)7743............2..................4.00
815743477743............2..................4.00
73477317743.........22..................3.50
73468017743.........2.....................3.00
734405a177413......131...............3.00
81549927743113......2...1.........3.00
73449927743115221...............2.50
734500177432123.....................1.75
81577317743413........................1.25
8155001774311...........................0.50
815496377431..............................0.00
Totals(68)10516189442.........2.72
SUMMARY.
Races.Grades of boot in offspring, reduced to percentages.
012345678910Average.
Cochins.......0.51.51.54.04.512.123.630.721.68.24
Dark Brahmas..........3.33.36.624.64.99.814.832.87.62
Silkie.14.87.423.526.513.25.95.92.9.........2.72

An inspection of table 31 shows that, in respect to booting, the Cochins and Dark Brahmas are clearly closely related to each other. Owing to smaller numbers and to other circumstances that will be discussed later, the results are less regular in the Dark Brahma offspring, but in both the range is from 2 or 3 upward to 10, with a great preponderance in grades above 5. In the Silkies, on the other hand, the greatest frequency is found in grades below 5. This difference is correlated with a difference of the parents, for the commonest grades of the parents of the Cochins are between 6 and 10, of the Dark Brahmas between 5 and 9, and of the Silkies between 1 and 3. These results suggest that the Silkie is typically heterozygous in boot, producing 25 per cent recessives (boot of grade 4-7) and 75 per cent dominant (0, 1) and heterozygous (2, 3). We shall see that this hypothesis receives support from all Silkie matings.

Inside of any part of this table it appears that, on the whole, as the average grade of the boot in the progeny diminishes that of the parentage diminishes, although the correlation is by no means perfect. Thus the average of the parental grades in the first part of table 31, A (which is arranged in descending order of the averages of the offspring) is 8.5; in the lower half, 7.4. The average of parental grades in the upper half of table 31, B is 6.4; in the lower half 5.5. In table 31, C the grades are 2.9 and 2.3, respectively. This correlation indicates, without exactly measuring, heredity in grade of booting.

Table 32 shows the results of crosses between Cochins (high grade of boot) and Silkies (low grade).

Table 32.—Distribution of boot-grades between a high and low grade of boot in parents.

HIGH AND LOW GRADE OF BOOT IN PARENTS.
Pen No.Mother.Father.Grade of boot in offspring.
No.Gen.Races.Gra.No.Gen.Race.Gra.012345678910Aver-
age.
8515567PBl. × Bf. C.9P7526Silkie.3............2.........3358.15
8513410PDo.9P7526Do.3...............4321617.29
8516956PDo.87526PDo.3............33...22...57.13
8512073PDo.77526PDo.3...1...11...111326.91
8512299PDo.77526PDo.3............2211......36.78
851840PBf. C.107526PDo.3............1...1......1...6.33
8511002PDo.87526PDo.3.........312124116.27
815131PBk. C. 10774PDo.4.........311221126.23
851841PBf. C.107526PDo.3............1...1...1......6.00
851838PDo.87526PDo.3.........4243......225.65
Totals (116)01011141613101317216.77

So far as the average grade of boot in offspring goes, this table stands between that of the Cochins (table 31, A) and that of the Silkies (table 31, C). But what is especially striking is the apparent dimorphism revealed in the line of totals. There is one (empirical) mode at 10, corresponding with that of the Cochins, and a second clear mode at 5, corresponding to that of the Silkies. If we assume the Cochin to be homozygous in boot (RR) and the Silkie to be heterozygous in boot, then we can interpret the high mode as extracted recessives, the median mode as heterozygotes.