160
A. D. BONEP
development (Hasegawa, 1962). The depopulation rates of young
stages of the immersed forms is greater during summer and autumn.
Annual growth of the blade shows one period of fast and one period
of slow growth during each annual cycle. Growth in frond width is
more noticeable during the second and third years, and reaches its
maximum between May and August in the third year of the plant’s
life. The phases of fast and slow growth vary with the age of the plant.
Thus the fast growth period in the 1st year is from March to July, and
is most rapid in April and May. In the 2nd year this phase of rapid
growth lasts from January to July, and in the 3rd year from December
until the following August. In most years the spring and early summer
are the main periods of rapid growth, and the slowest growth takes
place between August and October. The plants reach their maximum
weight in the rapid growth phase in the 3rd year of development. Plants
of L. angustata survive for some three years in their shore habitats, and
the annual growth of the blade results in the previous year’s blade
gradually wearing away at the new blade tip. Each year’s growth of
the plant is accompanied by the production of new whorls of haptera
at the base of the stipe.
Sporangia of L. angustata appear on the blade early in October in
the 1st year of growth, continuing until March of the next year.
During the 2nd year, sporangia appear in July, the peak period of
spore production being in October, and tailing-off into January. I n the
3rd-year plant the sporangia appear in June, and continue to be fertile
until January. Harvesting of the 3rd-year plants will allow ample spore
productivity in the first 2 years of growth, and enable adequate
establishment of gametophytes. Sporophyte depopulation is at a
greater rate during the spring of the first year of growth, viz. 96.6%,
although this falls to 77.5% after 15 months. A seasonal variation in
frond weight is also observed with L. angwtata, with maximum weight
in June and minimum weight between November and April.
10. Undaria
Recent data on the commercially important Undaria plants have
described two species, Undaria undarioides and Undaria pinnatiJida.
Segi and Kida (1957) studied the effects of certain environmental
factors on the growth of gametophytes of Undaria undarioides, obtaining
better growth at 2 200-3 300 lux than in “ full ” sunlight (4 500 lux).
Very slow growth was obtained at 400 lux, and although gametophytes
were successfully germinated in the dark, they were less viable than
those obtained in the light. The gametophytes of Undaria would appear
to show a much higher degree of tolerance to light than those of
A. D. BONEP
development (Hasegawa, 1962). The depopulation rates of young
stages of the immersed forms is greater during summer and autumn.
Annual growth of the blade shows one period of fast and one period
of slow growth during each annual cycle. Growth in frond width is
more noticeable during the second and third years, and reaches its
maximum between May and August in the third year of the plant’s
life. The phases of fast and slow growth vary with the age of the plant.
Thus the fast growth period in the 1st year is from March to July, and
is most rapid in April and May. In the 2nd year this phase of rapid
growth lasts from January to July, and in the 3rd year from December
until the following August. In most years the spring and early summer
are the main periods of rapid growth, and the slowest growth takes
place between August and October. The plants reach their maximum
weight in the rapid growth phase in the 3rd year of development. Plants
of L. angustata survive for some three years in their shore habitats, and
the annual growth of the blade results in the previous year’s blade
gradually wearing away at the new blade tip. Each year’s growth of
the plant is accompanied by the production of new whorls of haptera
at the base of the stipe.
Sporangia of L. angustata appear on the blade early in October in
the 1st year of growth, continuing until March of the next year.
During the 2nd year, sporangia appear in July, the peak period of
spore production being in October, and tailing-off into January. I n the
3rd-year plant the sporangia appear in June, and continue to be fertile
until January. Harvesting of the 3rd-year plants will allow ample spore
productivity in the first 2 years of growth, and enable adequate
establishment of gametophytes. Sporophyte depopulation is at a
greater rate during the spring of the first year of growth, viz. 96.6%,
although this falls to 77.5% after 15 months. A seasonal variation in
frond weight is also observed with L. angwtata, with maximum weight
in June and minimum weight between November and April.
10. Undaria
Recent data on the commercially important Undaria plants have
described two species, Undaria undarioides and Undaria pinnatiJida.
Segi and Kida (1957) studied the effects of certain environmental
factors on the growth of gametophytes of Undaria undarioides, obtaining
better growth at 2 200-3 300 lux than in “ full ” sunlight (4 500 lux).
Very slow growth was obtained at 400 lux, and although gametophytes
were successfully germinated in the dark, they were less viable than
those obtained in the light. The gametophytes of Undaria would appear
to show a much higher degree of tolerance to light than those of