FEATHERS AND PATTERNS
19
of the barb ridges proper are also destined not to form part of the
feather proper (but their cell walls may remain as important "sculpturing" of the surface; compare the Oberhauchen
of reptiles; Maderson,
1965).
Expiants of collar region (see Fig. 3) will also form barb ridges
in vitro, provided that no sheath is removed with them. The sheath, as
well as carrying infection, seems to restrict the slight "turbulence" necessary for the cells to adapt to their new local geography. These barb
ridges are formed at various angles to their normal future position in
these collar pieces and, in all probability, depend for their orientation on
accidental oriented trauma to the expiants. Some statistical bias toward the "right" orientation in the early series is probably entirely
attributable to the vital staining of the proximal ends of the collar in
these series. Midventral collar has, however, a strong (but not overwhelming) tendency to form "ventral triangles" (6 out of 16 cases which
did form ridges) even in those feathers which form a iter-feathers. This
result is surprising since the most proximal ventral part of the plucked
pinfeather collar would be expected to produce after-feather rather than
vane edges (compare Figs. 3 and 8). Perhaps the after-feather anläge lies
below the plane of separation of many such pinfeathers. This would account for the result, but is a rather facile excuse and has not been tested
further as yet.
More interesting is the variation in the periodicity of such barb ridges
produced in culture. Examination of hundreds of such expiants cultured
for a pigmentation experiment revealed that the periodicity varied from
10 to 16.4 barb ridges per millimeter even in expiants from the same kind
of feather. (Ventral barb ridges may be narrower than the dorsal, in vivo,
but their periodicity is the same.) On the other hand, there was little
variation between the expiants in any one series. Some culture condition
was, therefore, suspect as the agent of this variation. Further trials were
hampered by the refusal of the expiants to form barb ridges in a whole
variety of media and culture conditions; they either grew profusely as
epitheliocyte sheets or keratinized rapidly as flakes or solid masses.
Table I gives the composition of various media which did not work, as
well as the one (method 1 in Table I) which did and does. Since variation in chemical composition of the medium so easily results in the failure of the system under consideration, it was decided to standardize the
composition as far as was possible in this kind of biological work. Temperature was considered a useful experimental parameter to vary, and
preliminary results showed that this gave quite dramatic effects over
a wide range (Fig. 9).
Thirty Brown Leghorn cockerels, 14^17 days old, were castrated; of
19
of the barb ridges proper are also destined not to form part of the
feather proper (but their cell walls may remain as important "sculpturing" of the surface; compare the Oberhauchen
of reptiles; Maderson,
1965).
Expiants of collar region (see Fig. 3) will also form barb ridges
in vitro, provided that no sheath is removed with them. The sheath, as
well as carrying infection, seems to restrict the slight "turbulence" necessary for the cells to adapt to their new local geography. These barb
ridges are formed at various angles to their normal future position in
these collar pieces and, in all probability, depend for their orientation on
accidental oriented trauma to the expiants. Some statistical bias toward the "right" orientation in the early series is probably entirely
attributable to the vital staining of the proximal ends of the collar in
these series. Midventral collar has, however, a strong (but not overwhelming) tendency to form "ventral triangles" (6 out of 16 cases which
did form ridges) even in those feathers which form a iter-feathers. This
result is surprising since the most proximal ventral part of the plucked
pinfeather collar would be expected to produce after-feather rather than
vane edges (compare Figs. 3 and 8). Perhaps the after-feather anläge lies
below the plane of separation of many such pinfeathers. This would account for the result, but is a rather facile excuse and has not been tested
further as yet.
More interesting is the variation in the periodicity of such barb ridges
produced in culture. Examination of hundreds of such expiants cultured
for a pigmentation experiment revealed that the periodicity varied from
10 to 16.4 barb ridges per millimeter even in expiants from the same kind
of feather. (Ventral barb ridges may be narrower than the dorsal, in vivo,
but their periodicity is the same.) On the other hand, there was little
variation between the expiants in any one series. Some culture condition
was, therefore, suspect as the agent of this variation. Further trials were
hampered by the refusal of the expiants to form barb ridges in a whole
variety of media and culture conditions; they either grew profusely as
epitheliocyte sheets or keratinized rapidly as flakes or solid masses.
Table I gives the composition of various media which did not work, as
well as the one (method 1 in Table I) which did and does. Since variation in chemical composition of the medium so easily results in the failure of the system under consideration, it was decided to standardize the
composition as far as was possible in this kind of biological work. Temperature was considered a useful experimental parameter to vary, and
preliminary results showed that this gave quite dramatic effects over
a wide range (Fig. 9).
Thirty Brown Leghorn cockerels, 14^17 days old, were castrated; of