188
A. D. BONEY
sporeling is parallel with, or at an oblique plane to the substratum and
to the longitudinal axis of the germ tube, with the result that upper
and lower cells are formed. The cells which subsequently develop from
the uppermost cell become the first part of the creeping stem of the
erect frond. Branching takes place at an early stage in germling
development, so that two axes may arise, an early indication of the
vigorous branching shown by the adult plant. Prostrate branches also
arise at a very early stage in development. Changes in the salinity of
the medium appear to have little serious effect on the early growth of
the germlings, although some influence is recorded on the primary
rhizoids. Early vertical growth of the germling is soon followed by the
production of secondary shoots from the main axis, and these give rise
to creeping stolons. Young plants of G . amansii show a slow growth
during the summer, autumn and winter, but develop much more
rapidly in the following spring, and secondary shoots are rapidly
formed from the basal portion of the frond.
8. Pterocladia
A taxonomic study of the European species Pterocladia cupillacea
has been recently reported by Dixon (1960). This species is utilized as a
source of agar in many parts of the world, so that all aspects of its
biology are of interest. In the British Isles it shows a southern distribution, and appears to be sterile in the northern parts of its range. As
with the related Gelidium, form range is extremely variable, and is the
result of a complex interplay of both seasonal and environmental
factors. Observations on specimens from the British Isles, for example,
have shown that the spring initiation of new axes results in cylindrical
branches and these rapidly lengthen during spring and summer.
Linear growth slows down appreciably during the autumn and ceases
during the winter. A steady broadening of the fronds proceeds throughout the year, however, and this is particularly noticeable during the
winter months. Because of the perennial nature of the erect fronds the
lower laterals are discarded, so that the plants assume a dendroid
appearance (Dixon, 1963~). In Pterocladia, as with Gelidium pulchellum,
lateral branches of unlimited growth are always initiated at some
distance behind the apical cells of the main axis (Dixon, 1958b), so
that a regular dispositioning of laterals is observed.
The erect fronds arise from the prostrate creeping axis in a series
of dense tufts, a factor which will facilitate hand picking. Some
commercial usage of Pterocladia was reported from the British Isles
during the Second World War (Dixon, 1958b). The plant is fertile in
the southern parts of its range, and the fronds are much larger, so that
A. D. BONEY
sporeling is parallel with, or at an oblique plane to the substratum and
to the longitudinal axis of the germ tube, with the result that upper
and lower cells are formed. The cells which subsequently develop from
the uppermost cell become the first part of the creeping stem of the
erect frond. Branching takes place at an early stage in germling
development, so that two axes may arise, an early indication of the
vigorous branching shown by the adult plant. Prostrate branches also
arise at a very early stage in development. Changes in the salinity of
the medium appear to have little serious effect on the early growth of
the germlings, although some influence is recorded on the primary
rhizoids. Early vertical growth of the germling is soon followed by the
production of secondary shoots from the main axis, and these give rise
to creeping stolons. Young plants of G . amansii show a slow growth
during the summer, autumn and winter, but develop much more
rapidly in the following spring, and secondary shoots are rapidly
formed from the basal portion of the frond.
8. Pterocladia
A taxonomic study of the European species Pterocladia cupillacea
has been recently reported by Dixon (1960). This species is utilized as a
source of agar in many parts of the world, so that all aspects of its
biology are of interest. In the British Isles it shows a southern distribution, and appears to be sterile in the northern parts of its range. As
with the related Gelidium, form range is extremely variable, and is the
result of a complex interplay of both seasonal and environmental
factors. Observations on specimens from the British Isles, for example,
have shown that the spring initiation of new axes results in cylindrical
branches and these rapidly lengthen during spring and summer.
Linear growth slows down appreciably during the autumn and ceases
during the winter. A steady broadening of the fronds proceeds throughout the year, however, and this is particularly noticeable during the
winter months. Because of the perennial nature of the erect fronds the
lower laterals are discarded, so that the plants assume a dendroid
appearance (Dixon, 1963~). In Pterocladia, as with Gelidium pulchellum,
lateral branches of unlimited growth are always initiated at some
distance behind the apical cells of the main axis (Dixon, 1958b), so
that a regular dispositioning of laterals is observed.
The erect fronds arise from the prostrate creeping axis in a series
of dense tufts, a factor which will facilitate hand picking. Some
commercial usage of Pterocladia was reported from the British Isles
during the Second World War (Dixon, 1958b). The plant is fertile in
the southern parts of its range, and the fronds are much larger, so that