BIOLOQY OF SEAWEEDS O F ECONOMIC IMPORTANCE
159
winter, and by January the production of new blade tissue outpaced
the rate of defoliation of the old. General observations indicated that
the plants are 3 years old before sporangia are produced.
Laminaria japonica. Various aspects of the seasonal life of Laminaria japonica in relation to environmental factors have been reported
by Tseng et al. (1955a, 1957). In cultivation areas in north China the
main growth season extends from November to June and settlement of
spores on " collectors " for purposes of cultivation is possible over much
the same period. During the main growth season blades 3-4 m in length,
25-30 cm wide and 2-3 mm in thickness may be obtained, but this
varies along the coastline depending on the quantities of available
nutrients. When surface temperatures of the sea remain below 20°C
two to three weeks elapse between liberation of spores and development
of very young sporophytes. Frequently there is intensive competition
on the " collectors " with smaller algae (e.g. Ectocarpus sp.) which
grow vigorously at 20°C. Thus if the very young sporophytes are kept
at 10°C under controlled conditions and then placed in the open sea
where the temperatures fall below 20°C, this spatial competition with
smaller algae is not observed. The sporophytes, now several millimetres in size, are able to compete successfully with other algae. As a
result, the " haitai " yields are almost doubled. Improved growth of
the plants was also obtained by cultivating young sporophytes in racks
in the near vicinity of earthenware vessels containing NaNO,, Na,PO,,
NH,NO, and apatite powder. With the gradual outflow of nutrients
into the sea a marked enhancement of growth was observed over a
94-day period. The mean dry weight of thalli grown in this way was
32.2 g, having shown a daily increase in fresh weight of 363.2 mg. By
contrast, control material showed a mean dry weight of 7-9 g, and a
daily incremental change of fresh weight of 89 mg. It was estimated
that 1 kg of " haitai " required 1.01 kg of " nitrogen " fertilizer. These
methods certainly offer scope for further exploitation of fertilization
techniques.
The factor of competition with other algae referred to above is also
known in Japanese waters, where large-scale removal of Phyllospadix
is practised in order to encourage the spread of Laminaria plants.
L. japonica is harvested between July and October (Chapman, 1950).
Laminaria angustata. Two types of sporophyte have been observed,
the ovate-bladed winter type which remains immersed, and the
lanceolate-bladed spring sporophyte which is intertidal. Certain
aspects of the two forms are distinguishable at the earliest stages of
159
winter, and by January the production of new blade tissue outpaced
the rate of defoliation of the old. General observations indicated that
the plants are 3 years old before sporangia are produced.
Laminaria japonica. Various aspects of the seasonal life of Laminaria japonica in relation to environmental factors have been reported
by Tseng et al. (1955a, 1957). In cultivation areas in north China the
main growth season extends from November to June and settlement of
spores on " collectors " for purposes of cultivation is possible over much
the same period. During the main growth season blades 3-4 m in length,
25-30 cm wide and 2-3 mm in thickness may be obtained, but this
varies along the coastline depending on the quantities of available
nutrients. When surface temperatures of the sea remain below 20°C
two to three weeks elapse between liberation of spores and development
of very young sporophytes. Frequently there is intensive competition
on the " collectors " with smaller algae (e.g. Ectocarpus sp.) which
grow vigorously at 20°C. Thus if the very young sporophytes are kept
at 10°C under controlled conditions and then placed in the open sea
where the temperatures fall below 20°C, this spatial competition with
smaller algae is not observed. The sporophytes, now several millimetres in size, are able to compete successfully with other algae. As a
result, the " haitai " yields are almost doubled. Improved growth of
the plants was also obtained by cultivating young sporophytes in racks
in the near vicinity of earthenware vessels containing NaNO,, Na,PO,,
NH,NO, and apatite powder. With the gradual outflow of nutrients
into the sea a marked enhancement of growth was observed over a
94-day period. The mean dry weight of thalli grown in this way was
32.2 g, having shown a daily increase in fresh weight of 363.2 mg. By
contrast, control material showed a mean dry weight of 7-9 g, and a
daily incremental change of fresh weight of 89 mg. It was estimated
that 1 kg of " haitai " required 1.01 kg of " nitrogen " fertilizer. These
methods certainly offer scope for further exploitation of fertilization
techniques.
The factor of competition with other algae referred to above is also
known in Japanese waters, where large-scale removal of Phyllospadix
is practised in order to encourage the spread of Laminaria plants.
L. japonica is harvested between July and October (Chapman, 1950).
Laminaria angustata. Two types of sporophyte have been observed,
the ovate-bladed winter type which remains immersed, and the
lanceolate-bladed spring sporophyte which is intertidal. Certain
aspects of the two forms are distinguishable at the earliest stages of