BIOLOGY OF SEAWEEDS O F ECONOMIC IMPORTANCE
165
fusion has been considered, and the lack of any concrete evidence reemphasized. The need for a re-examination of " spore terminology "
was also stressed. Thus the large spores produced by the Porphyra
thallus were called a-spores, and the smaller ones ,!?-spores. Observations on Porphyra umbilicalis have shown that spore release and
germination are optimal in May and June, and again in October and
early November. The vigour of spore production was found to vary
appreciably with habitat.
Germination and growth of the a-spores were best obtained at low
temperatures (5"-7"C), and in a light regime of 80-100 lux for 8 h/day.
Culture at 1100 lux for 12 h/day at 20°C resulted in bleaching and
deterioration of the cells. The growing Conchocelis-phase produced
terminal monosporangia, and the liberated spores then gave rise to
more Conchocelis filaments on germination. Conchospore-bearing
branches were observed in filaments which were kept for several
months at higher temperatures and increased day length. It seems
likely that the monospores and conchospores are different structures ;
and whilst the conchospores can give rise to young plants similar to
those of the leafy thalli, under certain environmental conditions they
produce again the Conchocelis-phase, in common with the liberated
monospores. Dwarf plants have also been observed which are intolerant
of raised temperatures, increased day lengths and higher light intensities. The northern plants of Porphyra umbilicalis show adaptations to
a wide range of environmental conditions. The a-spores are produced
asexually. The ,!?-spores appear functionless, and in the absence of any
adequate cytological data the occurrence of a gametic fusion must be a
matter of conjecture.
2. Techniques used in the large-scale cultivation of Porphyra
In the more traditional methods bundles of twigs were planted in
suitable inshore areas to serve as substrata for spore settlement. In
addition the cultivation of plants in intertidal habitats was practised,
notably by the " weeding-out " of competitors. Modern techniques
include much which was of older foundation, and in intertidal areas new
substrata for spore settlements are obtained by concreting the rock face,
placing boulders or concrete structures in the sea, and by blowing-up
rocks in suitable habitats (Rurogi, 1963a). Methods of inshore cultivation still include the use of 'I hibi " of bamboo brush, and of " blinds "
of split bamboo bound together. Alternatively nets of mesh size 15 cm
X 15 cm made from synthetic plastic fibre, or from coconut palm or
hemp palm are used. The " hibi " are spread in the sea at suitable
times of the year (see p. 167 et seq.). The '' hibi " are usually spread at
165
fusion has been considered, and the lack of any concrete evidence reemphasized. The need for a re-examination of " spore terminology "
was also stressed. Thus the large spores produced by the Porphyra
thallus were called a-spores, and the smaller ones ,!?-spores. Observations on Porphyra umbilicalis have shown that spore release and
germination are optimal in May and June, and again in October and
early November. The vigour of spore production was found to vary
appreciably with habitat.
Germination and growth of the a-spores were best obtained at low
temperatures (5"-7"C), and in a light regime of 80-100 lux for 8 h/day.
Culture at 1100 lux for 12 h/day at 20°C resulted in bleaching and
deterioration of the cells. The growing Conchocelis-phase produced
terminal monosporangia, and the liberated spores then gave rise to
more Conchocelis filaments on germination. Conchospore-bearing
branches were observed in filaments which were kept for several
months at higher temperatures and increased day length. It seems
likely that the monospores and conchospores are different structures ;
and whilst the conchospores can give rise to young plants similar to
those of the leafy thalli, under certain environmental conditions they
produce again the Conchocelis-phase, in common with the liberated
monospores. Dwarf plants have also been observed which are intolerant
of raised temperatures, increased day lengths and higher light intensities. The northern plants of Porphyra umbilicalis show adaptations to
a wide range of environmental conditions. The a-spores are produced
asexually. The ,!?-spores appear functionless, and in the absence of any
adequate cytological data the occurrence of a gametic fusion must be a
matter of conjecture.
2. Techniques used in the large-scale cultivation of Porphyra
In the more traditional methods bundles of twigs were planted in
suitable inshore areas to serve as substrata for spore settlement. In
addition the cultivation of plants in intertidal habitats was practised,
notably by the " weeding-out " of competitors. Modern techniques
include much which was of older foundation, and in intertidal areas new
substrata for spore settlements are obtained by concreting the rock face,
placing boulders or concrete structures in the sea, and by blowing-up
rocks in suitable habitats (Rurogi, 1963a). Methods of inshore cultivation still include the use of 'I hibi " of bamboo brush, and of " blinds "
of split bamboo bound together. Alternatively nets of mesh size 15 cm
X 15 cm made from synthetic plastic fibre, or from coconut palm or
hemp palm are used. The " hibi " are spread in the sea at suitable
times of the year (see p. 167 et seq.). The '' hibi " are usually spread at