BIOLOGY OF SEAWEEDS O F ECONOMIC IMPORTANCE
187
of the different types of fruiting plant with depth. The smaller number
of plants bearing sex organs were thought to be due either to a failure
of the tetraspores to germinate, or to death of the young germlings.
Vegetative growth by the tetrasporophytes was most vigorous, and three
principal periods of branch growth and regeneration were observed
during the course of the year, in February, July and October. Each of
these times appear to follow periods of intense surf activity which
probably cause large numbers of damaged fronds, and so stimulate
regenerative growth. Production of new erect fronds from the attaching
branches shows no clear seasonal periodicity, although there were indications of greater vegetative activity in March and early July. The conclusion was drawn that, in the absence of any distinct seasonal periodicity in fruiting behaviour, and because of the vigorous regenerative
growth, no specific season need be chosen for harvesting. However,
Cooper and Johnstone (1944) reported that there was a seasonal
variation in the quantities of agar extracted per dry weight of plant,
and that this was at a maximum in May, June and July, the months
with maximum photosynthetic activity.
The regeneration properties of Gelidium amansii, the principal
source of agar in Japan, were studied many years ago by Okamura
(191 l), who scattered small fragments of frondage along the shore, and
found that in many instances these small fragments quickly became
attached to pieces of stone and regenerated new vegetative apices and
attachment organs. More recent work on the propagation of this
species by Yamasaki and Osuga (1960) studied the succession of plants
on freshly set stones in the culture grounds. After 2 years the plants
bearing carposporophytes outnumbered those bearing tetrasporangia by
a ratio which approached 2 : 1, but after 4 years this ratio was almost
exactly reversed, and became much the same as that found with plants
growing on neighbouring regions of the shore which were left untouched.
The best time for harvesting G. amansii appeared to be between August
and October, probably coinciding with the period of maximum photosynthetic activity.
Spore productivity is an important aspect of the seasonal life of the
seaweeds. Dixon (1958b) was unable to obtain spore germination for
Gelidium pulchellum and G. lutifolium. Various reports are available
about the early development of Gelidium sp., and certain of the observations are relevant to the growth of the adult plants. Early developmental stages have been described by Chemin (1937), Katada (1949,
1955), Suto (1950), Yamasaki (1960) and Boillot (1963). All observers
agree that the early stages of germination follow the release of the
spore contents into an indirect germ tube. The first division of the
187
of the different types of fruiting plant with depth. The smaller number
of plants bearing sex organs were thought to be due either to a failure
of the tetraspores to germinate, or to death of the young germlings.
Vegetative growth by the tetrasporophytes was most vigorous, and three
principal periods of branch growth and regeneration were observed
during the course of the year, in February, July and October. Each of
these times appear to follow periods of intense surf activity which
probably cause large numbers of damaged fronds, and so stimulate
regenerative growth. Production of new erect fronds from the attaching
branches shows no clear seasonal periodicity, although there were indications of greater vegetative activity in March and early July. The conclusion was drawn that, in the absence of any distinct seasonal periodicity in fruiting behaviour, and because of the vigorous regenerative
growth, no specific season need be chosen for harvesting. However,
Cooper and Johnstone (1944) reported that there was a seasonal
variation in the quantities of agar extracted per dry weight of plant,
and that this was at a maximum in May, June and July, the months
with maximum photosynthetic activity.
The regeneration properties of Gelidium amansii, the principal
source of agar in Japan, were studied many years ago by Okamura
(191 l), who scattered small fragments of frondage along the shore, and
found that in many instances these small fragments quickly became
attached to pieces of stone and regenerated new vegetative apices and
attachment organs. More recent work on the propagation of this
species by Yamasaki and Osuga (1960) studied the succession of plants
on freshly set stones in the culture grounds. After 2 years the plants
bearing carposporophytes outnumbered those bearing tetrasporangia by
a ratio which approached 2 : 1, but after 4 years this ratio was almost
exactly reversed, and became much the same as that found with plants
growing on neighbouring regions of the shore which were left untouched.
The best time for harvesting G. amansii appeared to be between August
and October, probably coinciding with the period of maximum photosynthetic activity.
Spore productivity is an important aspect of the seasonal life of the
seaweeds. Dixon (1958b) was unable to obtain spore germination for
Gelidium pulchellum and G. lutifolium. Various reports are available
about the early development of Gelidium sp., and certain of the observations are relevant to the growth of the adult plants. Early developmental stages have been described by Chemin (1937), Katada (1949,
1955), Suto (1950), Yamasaki (1960) and Boillot (1963). All observers
agree that the early stages of germination follow the release of the
spore contents into an indirect germ tube. The first division of the