BIOLOGY O F SEAWEEDS O F ECONOMIC IMPORTANCE
169
A somewhat different interpretation of the life-history has been
given by Tseng and Chang (1955a, b) for P. tenera cultivated in China.
It is also claimed that a sexual fusion does occur in the life cycle. The
cell constituting the " carpogonium " was said to send out a filamentous
projection, subsequently withdrawn, to which the spermatia adhere.
Passage of the contents of the spermatium into the " carpogonium "
was described but actual fusion of the cell nuclei was not observed.
Tseng and Chang stated that meiosis occurred in the carposporangium,
so that haploid " carpospores " would then be produced. Two peaks of
" carpospore " production were described, the first starting in late
November and continuing through December, and the second extending through April and May, corresponding to the initial and final stages
of growth of the leafy thalli in the culture " grounds ". The leafy
thallus reproduces asexually by means of monospores when sea temperatures lie between 15"-17"C; the production of sexual cells is observed when sea temperatures remain below 15°C. Apparently both
monosporangia and I' carposporangia " have been found on occasions
on the same thallus due to a particular combination of environmental
factors. The Conchocelis-phase grows throughout the summer, but is
reported to commence spore liberation in early summer (sea temperatures 15"-20°C). The Porphyra plants formed as a result of the germination of the early summer spores are of a dwarf form, whereas the monospores produced by the Conchocelis-phase during autumn grow into the
normal leafy thalli. The summer dwarf plants have smaller cells and
produce monospores which throughout the summer months give rise to
dwarf plants. Whilst dwarf plants are produced through the early part
of the autumn, they later grow into normal thalli. These " summer
dwarfs '' do not seem to have been described in Japan, and Tseng and
Chang (1955a) point out that these dwarf plants are not an obligatory
phase in the life-history. The plants from both regions appear to grow
best during the autumn when there is a fall in sea temperature, and when
there is the shortest growth period (1 month) in order to obtain a plant
of harvestable size.
Various factors known to influence the early development of
Porphyra have also been investigated, (Hasegawa et al., 1952 ; Iwasaki
and Matsudaira, 1958 ; Matsumoto, 1959 ; Iwasaki, 1961). Healthy
growth of the thalli was obtained in media enriched with nitrate and
phosphate, trace elements, and with organic nutrients such as Vitamin
BI2, thiamine and biotin. Young " buds " appeared to require iron
enrichment of the medium. Incandescent light allowed growth under
culture conditions, although natural sunlight was preferable ; fluorescent light proved harmful to the young plants. A light regime of 8-10 h
169
A somewhat different interpretation of the life-history has been
given by Tseng and Chang (1955a, b) for P. tenera cultivated in China.
It is also claimed that a sexual fusion does occur in the life cycle. The
cell constituting the " carpogonium " was said to send out a filamentous
projection, subsequently withdrawn, to which the spermatia adhere.
Passage of the contents of the spermatium into the " carpogonium "
was described but actual fusion of the cell nuclei was not observed.
Tseng and Chang stated that meiosis occurred in the carposporangium,
so that haploid " carpospores " would then be produced. Two peaks of
" carpospore " production were described, the first starting in late
November and continuing through December, and the second extending through April and May, corresponding to the initial and final stages
of growth of the leafy thalli in the culture " grounds ". The leafy
thallus reproduces asexually by means of monospores when sea temperatures lie between 15"-17"C; the production of sexual cells is observed when sea temperatures remain below 15°C. Apparently both
monosporangia and I' carposporangia " have been found on occasions
on the same thallus due to a particular combination of environmental
factors. The Conchocelis-phase grows throughout the summer, but is
reported to commence spore liberation in early summer (sea temperatures 15"-20°C). The Porphyra plants formed as a result of the germination of the early summer spores are of a dwarf form, whereas the monospores produced by the Conchocelis-phase during autumn grow into the
normal leafy thalli. The summer dwarf plants have smaller cells and
produce monospores which throughout the summer months give rise to
dwarf plants. Whilst dwarf plants are produced through the early part
of the autumn, they later grow into normal thalli. These " summer
dwarfs '' do not seem to have been described in Japan, and Tseng and
Chang (1955a) point out that these dwarf plants are not an obligatory
phase in the life-history. The plants from both regions appear to grow
best during the autumn when there is a fall in sea temperature, and when
there is the shortest growth period (1 month) in order to obtain a plant
of harvestable size.
Various factors known to influence the early development of
Porphyra have also been investigated, (Hasegawa et al., 1952 ; Iwasaki
and Matsudaira, 1958 ; Matsumoto, 1959 ; Iwasaki, 1961). Healthy
growth of the thalli was obtained in media enriched with nitrate and
phosphate, trace elements, and with organic nutrients such as Vitamin
BI2, thiamine and biotin. Young " buds " appeared to require iron
enrichment of the medium. Incandescent light allowed growth under
culture conditions, although natural sunlight was preferable ; fluorescent light proved harmful to the young plants. A light regime of 8-10 h