BIOLOGY OF SEAWEEDS OF ECONOMIC IMPORTANCE
195
mid-December, and the peak period of discharge is also a relatively
short one (between 26th December to 8th January). Male plants are
conspicuous during autumn, winter and spring, and spermatium
production extends from December to April. Carpogonia are initiated
in January and fertilization soon follows. Maturation of the carposporophyte is a protracted process, and carpospore liberation takes place
nearly 12 months after fertilization. I n both cases, spore emission
periods are short, so that any recruitment of spore materid to the
free-living population would similarly be of short duration.
14. Gracilaria
Gracilaria verrucosa is the species mainly used as a source of extractives, particularly on the south-east coast of the United States (Tseng,
1947) and in Australia and New Zealand. A small agar industry has
also been established in South Africa (Isaac and Molteno, 1963) and in
Japan. Gracilaria verrucosa is a species of world-wide distribution, and
plants reach an appreciable size in Australia and on the Egyptian
coast. Tseng (1947) reports that plants up to 6 ft in length may be
found in suitable habitats on the coast of North Carolina, and plants up
to 12 ft long have been reported from near Vancouver, British Columbia.
It appears to grow best in sheltered bays, particularly in river estuaries
with sandy or muddy floors, and where there is shelter from wave action.
action. Jones (19594 found that plants in North Wales grew best in
localities with strong water currents, but also with shelter from wave
action. I n many localities in the British Isles the plant is a common
component of the sand-pool flora. The species has been recorded in
Norway only since 1935, growing unattached on muddy substrata in
land-locked bays where in the summer water temperatures can reach
16"-20"C. The plants were found to be able to tolerate water with high
H,S content (Stokke, 1966), but plants are rarely more than 10-16 cm
in length.
Variations in size, colour and structure have been reported, and
length of frond and width of branch have been used as a means of
distinguishing between the different forms (May, 1948 ; Jones, 1962).
Whilst frequently growing on rocky substrata and attached by a
discoid holdfast, free-floating plants are frequently reported. Pillsbury (1950) described how Gracilaria plants could become cemented to
calcareous worm tubes and the plants can reach lengths of many feet
without a distinct holdfast system, and can also be many kilograms in
weight. Ohmi (1958) reported from Japan that Gracilaria occurred in
great profusion as a free-living plant in shallow turbid waters subject
195
mid-December, and the peak period of discharge is also a relatively
short one (between 26th December to 8th January). Male plants are
conspicuous during autumn, winter and spring, and spermatium
production extends from December to April. Carpogonia are initiated
in January and fertilization soon follows. Maturation of the carposporophyte is a protracted process, and carpospore liberation takes place
nearly 12 months after fertilization. I n both cases, spore emission
periods are short, so that any recruitment of spore materid to the
free-living population would similarly be of short duration.
14. Gracilaria
Gracilaria verrucosa is the species mainly used as a source of extractives, particularly on the south-east coast of the United States (Tseng,
1947) and in Australia and New Zealand. A small agar industry has
also been established in South Africa (Isaac and Molteno, 1963) and in
Japan. Gracilaria verrucosa is a species of world-wide distribution, and
plants reach an appreciable size in Australia and on the Egyptian
coast. Tseng (1947) reports that plants up to 6 ft in length may be
found in suitable habitats on the coast of North Carolina, and plants up
to 12 ft long have been reported from near Vancouver, British Columbia.
It appears to grow best in sheltered bays, particularly in river estuaries
with sandy or muddy floors, and where there is shelter from wave action.
action. Jones (19594 found that plants in North Wales grew best in
localities with strong water currents, but also with shelter from wave
action. I n many localities in the British Isles the plant is a common
component of the sand-pool flora. The species has been recorded in
Norway only since 1935, growing unattached on muddy substrata in
land-locked bays where in the summer water temperatures can reach
16"-20"C. The plants were found to be able to tolerate water with high
H,S content (Stokke, 1966), but plants are rarely more than 10-16 cm
in length.
Variations in size, colour and structure have been reported, and
length of frond and width of branch have been used as a means of
distinguishing between the different forms (May, 1948 ; Jones, 1962).
Whilst frequently growing on rocky substrata and attached by a
discoid holdfast, free-floating plants are frequently reported. Pillsbury (1950) described how Gracilaria plants could become cemented to
calcareous worm tubes and the plants can reach lengths of many feet
without a distinct holdfast system, and can also be many kilograms in
weight. Ohmi (1958) reported from Japan that Gracilaria occurred in
great profusion as a free-living plant in shallow turbid waters subject