BIOLOGY O F SEAWEEDS O F ECONOMIC IMPORTANCE
185
single apical meristematic cell. I n a number of field observations,
Dixon showed that several markedly different forms of erect frond, which
in some instances were characteristic of other species, could all be traced
to a common prostrate axis. Both the attaching branches and the erect
fronds are perennial structures, the prostrate branches in particular
showing a marked persistence in many shore sites. Whilst the state of
the erect fronds will vary to some extent with season, experiments have
shown that wholesale removal of the branches causes no diminution in
the vigour of the plant, nor of the number of branch primordia produced
in the following year. Thus whilst the extreme polymorphism of this
genus will continue to present appreciable difficulties in the taxmomic
field, the vigour of its growth and branch proliferation is an exceedingly
valuable feature for plants used as agarophytss.
The reproductive behaviour of the two species was also studied by
Dixon (195813). In both cases sexual plants and tetrasporophytes are
known, and the plants bearing tetrasporangia appear to be more
common. Male plants of G. pulchellum were not, in fact, collected in
the British Isles, although this could be a result of their small size and
lack of readily detectable characters. Observations on the seasonal
periodicity of fruiting by the species in the British Isles have shown that
although tetrasporangia are initiated in June and July, actual maturation and release of the spores is a protracted process which may run on
into the early part of the succeeding year. Male plants of G. latifolium
have been found during the autumn. Germlings have not been found in
the British material so far examined, and all young axes were traced
back to a perennial attaching structure.
The vigorous growth of frondage observed for the plants in the
British Isles seems to be paralleled by the species used as a source of
agar on the western coasts of the United States, i.e. Gelidium cartilagineum. This plant grows in sublittoral habitats as far north as Washington and is harvested in quantity at depths down to 40 to 50 ft on the
coast of California (Tseng, 1947). The branching of the erect fronds is
repeatedly pinnate, giving a fern-like appearance (Fig. 12), and the
branches can reach lengths of 4 to 5 ft, with a number of fronds arising
from a prostrate attaching branch. Harvesting is usually effected by
diving and hand-picking, although raking from boats has also been used.
Tseng remarked on the frequent association between dense beds of
the agarophyte and a species of the goldfish Hypsypops which might
serve as a “fisherman’s sign ”. These dense beds always tend to
occur on the seaward edges of rocky reefs where there is fairly intensive
wave action, and also where harvesting can be rather a hazardous
operation. Times of collecting the seaweed are therefore more condiA.M.B.-3
K
185
single apical meristematic cell. I n a number of field observations,
Dixon showed that several markedly different forms of erect frond, which
in some instances were characteristic of other species, could all be traced
to a common prostrate axis. Both the attaching branches and the erect
fronds are perennial structures, the prostrate branches in particular
showing a marked persistence in many shore sites. Whilst the state of
the erect fronds will vary to some extent with season, experiments have
shown that wholesale removal of the branches causes no diminution in
the vigour of the plant, nor of the number of branch primordia produced
in the following year. Thus whilst the extreme polymorphism of this
genus will continue to present appreciable difficulties in the taxmomic
field, the vigour of its growth and branch proliferation is an exceedingly
valuable feature for plants used as agarophytss.
The reproductive behaviour of the two species was also studied by
Dixon (195813). In both cases sexual plants and tetrasporophytes are
known, and the plants bearing tetrasporangia appear to be more
common. Male plants of G. pulchellum were not, in fact, collected in
the British Isles, although this could be a result of their small size and
lack of readily detectable characters. Observations on the seasonal
periodicity of fruiting by the species in the British Isles have shown that
although tetrasporangia are initiated in June and July, actual maturation and release of the spores is a protracted process which may run on
into the early part of the succeeding year. Male plants of G. latifolium
have been found during the autumn. Germlings have not been found in
the British material so far examined, and all young axes were traced
back to a perennial attaching structure.
The vigorous growth of frondage observed for the plants in the
British Isles seems to be paralleled by the species used as a source of
agar on the western coasts of the United States, i.e. Gelidium cartilagineum. This plant grows in sublittoral habitats as far north as Washington and is harvested in quantity at depths down to 40 to 50 ft on the
coast of California (Tseng, 1947). The branching of the erect fronds is
repeatedly pinnate, giving a fern-like appearance (Fig. 12), and the
branches can reach lengths of 4 to 5 ft, with a number of fronds arising
from a prostrate attaching branch. Harvesting is usually effected by
diving and hand-picking, although raking from boats has also been used.
Tseng remarked on the frequent association between dense beds of
the agarophyte and a species of the goldfish Hypsypops which might
serve as a “fisherman’s sign ”. These dense beds always tend to
occur on the seaward edges of rocky reefs where there is fairly intensive
wave action, and also where harvesting can be rather a hazardous
operation. Times of collecting the seaweed are therefore more condiA.M.B.-3
K