BIOLOGY O F SEAWEEDS O F ECONOMIC3 IMPORTANCE
167
plants 1 m in length have been recorded from the calm waters of the
" inner " seas. The fronds tend to grow paler with increasing age
except in regions which are particularly rich in nutrients. The plants
are monoecious, but those bearing only male organs are relatively
common. The male organs are borne in pale-coloured areas of the fronds,
situated either at the margins or scattered between the darker areas of
the frond which bear the " carpogonia ". The spermatangia bear 32-64
(sometimes 128) spermatia, and 4-8 " carpospores " are produced per
" carpogonium ". Examples in which the spermatangia and " carpogonia " are restricted to different areas of the frond have been described.
Where both organs are borne on the same frond the spermatangia
mature and release their contents before the " carpogonia " are fully
developed. Whilst the " carpogonia ) ' are identical with vegetative cells
in surface view they appear spindular in cross section, and Kurogi (1961)
stated that a thread-like connection was to be seen between a " carpogonium " and an attached spermatium. As the growth season terminates so a number of the " carpogonia " apparently abort, but in
inshore waters rich in nutrients cells are found in the " carpogonial "
region of the frond which produce spores, and these in turn give rise
to leafy thalli on germination.
In Matsushima Bay the best settlements are obtained when " hibi "
are spread from mid-September to early November. The young
" buds " which develop are at first filamentous (up to 260 p in length)
thence broadening by longitudinal cell division. " Hibi " spread after
mid-November fail to show young plants. The young " buds ) ' on the
" hibi " liberate monospores (" neutral spores ") at an early stage in
development, and these monospores also settle on the "hibi" and
their growth and development leads to dense settlements of young
plants (equal to 2000-3000 plants per 10 cm of bamboo thread).
Production of monospores continues into mid-November, and the
broader form of thallus observed with plants growing in inshore waters
is a result of the protracted spore production which truncates the thallus
apex. Small plants 1 cm in length appear after 1 month, and after 2
months lengths of 26 cm are recorded with frond width 7-6-10 cm. The
plants start to reach a harvestable size in late November and early
December, and a dense growth of plants on the " hibi " is then seen
until March. A rapid decline in the population is seen during April and
May.
" Carpogonia " and spermatangia appear on the thalli 3-6 cm in
length early in November, and production of " carpospores ) ' continues
until May. The " carpospores " produce the shell-boring Conchocelisphase on germination and the filaments of this stage in the life-history
167
plants 1 m in length have been recorded from the calm waters of the
" inner " seas. The fronds tend to grow paler with increasing age
except in regions which are particularly rich in nutrients. The plants
are monoecious, but those bearing only male organs are relatively
common. The male organs are borne in pale-coloured areas of the fronds,
situated either at the margins or scattered between the darker areas of
the frond which bear the " carpogonia ". The spermatangia bear 32-64
(sometimes 128) spermatia, and 4-8 " carpospores " are produced per
" carpogonium ". Examples in which the spermatangia and " carpogonia " are restricted to different areas of the frond have been described.
Where both organs are borne on the same frond the spermatangia
mature and release their contents before the " carpogonia " are fully
developed. Whilst the " carpogonia ) ' are identical with vegetative cells
in surface view they appear spindular in cross section, and Kurogi (1961)
stated that a thread-like connection was to be seen between a " carpogonium " and an attached spermatium. As the growth season terminates so a number of the " carpogonia " apparently abort, but in
inshore waters rich in nutrients cells are found in the " carpogonial "
region of the frond which produce spores, and these in turn give rise
to leafy thalli on germination.
In Matsushima Bay the best settlements are obtained when " hibi "
are spread from mid-September to early November. The young
" buds " which develop are at first filamentous (up to 260 p in length)
thence broadening by longitudinal cell division. " Hibi " spread after
mid-November fail to show young plants. The young " buds ) ' on the
" hibi " liberate monospores (" neutral spores ") at an early stage in
development, and these monospores also settle on the "hibi" and
their growth and development leads to dense settlements of young
plants (equal to 2000-3000 plants per 10 cm of bamboo thread).
Production of monospores continues into mid-November, and the
broader form of thallus observed with plants growing in inshore waters
is a result of the protracted spore production which truncates the thallus
apex. Small plants 1 cm in length appear after 1 month, and after 2
months lengths of 26 cm are recorded with frond width 7-6-10 cm. The
plants start to reach a harvestable size in late November and early
December, and a dense growth of plants on the " hibi " is then seen
until March. A rapid decline in the population is seen during April and
May.
" Carpogonia " and spermatangia appear on the thalli 3-6 cm in
length early in November, and production of " carpospores ) ' continues
until May. The " carpospores " produce the shell-boring Conchocelisphase on germination and the filaments of this stage in the life-history