BIOLOGY OF SEAWEEDS OF ECONOMIC IMPORTANCE
181
means. These observations are relevant to some earlier work by Drew
(1954a,b, 1958) who demonstrated that shells containing the Conchocelis filaments could " infect " other (sterilized) shells introduced
into the medium without physical contact between the two. It seems
likely that the cultural conditions used by Drew favoured the growth
of structures similar to those described by Iwasaki and Matsudaira.
Iwasaki and Matsudaira have also drawn attention to the marked
plasticity of the stages of Porphyra tenera under a wide range of
environmental conditions (see also Conway, 1964a,b,c, and p. 165).
Many of the conflicting data obtained by the study of Porphyra under
culture conditions is probably due to similar properties exhibited by
other species.
The importance of sea temperature and the onset or waning of
these different phases in the life-history has already been described.
Studies have also been made on the temperature conditions governing
formation of the sporangia on the Conchocelis filaments and release of
the spores (Kurogi, 1961 ; Kurogi and Hirano, 1956b ; Tseng and Chang,
195513,1956). Monosporangium formation by P . tenera was observedin a
temperature range of 15"-27"C, whilst for P . kuniedai the temperature
limits were 15"-25"C. Tseng and Chang (1955b, 1956), stated that whilst
sporangium formation was possible in a temperature range of 15"-30°C,
a period of lower temperatures ( 15"-2OoC) was necessary before spore
formation was observed in the sporangium.
Spore release by the Conchocelis-phase. The diurnal periodicity in
spore release by the shell-boring phase of P . tenera has been investigated
by Suto et al. (1954), Yamasaki (1954b), and Tseng and Chsng (1956). In
general, spore discharge commences in the morning in the first few hours
after sunrise and quickly reaches its peak (7-10 a.m. according to Suto ;
8-10 a.m. according to Tseng and Chang). Over 50% of the total
spores liberated during the day are released during the first few hours ;
in the later part of the day this productivity falls to 5 to 9% of the
overall daily spore output. Yamasaki stated that whilst the shedding
of spores commences at sunrise and continues apace for the next 2 or 3 h
on sunny days, on days with heavy cloud the copious output is delayed
for 2-3 h. Light reactions are evidently a necessary preliminary to
spore release from the sporangia. However Saito (1966a) considered
that increased sea temperature enhanced the rate of spore emission
along with changes in the level of illumination.
The temperature conditions governing spore emission have also been
studied. Release of spores, which is preceded by dissolution of the
sporangium wall, is most abundant at temperatures between 1 2"-20"C,
but is markedly reduced at temperatures of 9°C and 24°C (Fig. 11)
181
means. These observations are relevant to some earlier work by Drew
(1954a,b, 1958) who demonstrated that shells containing the Conchocelis filaments could " infect " other (sterilized) shells introduced
into the medium without physical contact between the two. It seems
likely that the cultural conditions used by Drew favoured the growth
of structures similar to those described by Iwasaki and Matsudaira.
Iwasaki and Matsudaira have also drawn attention to the marked
plasticity of the stages of Porphyra tenera under a wide range of
environmental conditions (see also Conway, 1964a,b,c, and p. 165).
Many of the conflicting data obtained by the study of Porphyra under
culture conditions is probably due to similar properties exhibited by
other species.
The importance of sea temperature and the onset or waning of
these different phases in the life-history has already been described.
Studies have also been made on the temperature conditions governing
formation of the sporangia on the Conchocelis filaments and release of
the spores (Kurogi, 1961 ; Kurogi and Hirano, 1956b ; Tseng and Chang,
195513,1956). Monosporangium formation by P . tenera was observedin a
temperature range of 15"-27"C, whilst for P . kuniedai the temperature
limits were 15"-25"C. Tseng and Chang (1955b, 1956), stated that whilst
sporangium formation was possible in a temperature range of 15"-30°C,
a period of lower temperatures ( 15"-2OoC) was necessary before spore
formation was observed in the sporangium.
Spore release by the Conchocelis-phase. The diurnal periodicity in
spore release by the shell-boring phase of P . tenera has been investigated
by Suto et al. (1954), Yamasaki (1954b), and Tseng and Chsng (1956). In
general, spore discharge commences in the morning in the first few hours
after sunrise and quickly reaches its peak (7-10 a.m. according to Suto ;
8-10 a.m. according to Tseng and Chang). Over 50% of the total
spores liberated during the day are released during the first few hours ;
in the later part of the day this productivity falls to 5 to 9% of the
overall daily spore output. Yamasaki stated that whilst the shedding
of spores commences at sunrise and continues apace for the next 2 or 3 h
on sunny days, on days with heavy cloud the copious output is delayed
for 2-3 h. Light reactions are evidently a necessary preliminary to
spore release from the sporangia. However Saito (1966a) considered
that increased sea temperature enhanced the rate of spore emission
along with changes in the level of illumination.
The temperature conditions governing spore emission have also been
studied. Release of spores, which is preceded by dissolution of the
sporangium wall, is most abundant at temperatures between 1 2"-20"C,
but is markedly reduced at temperatures of 9°C and 24°C (Fig. 11)