BIOLOGY O F SEAWEEDS O F ECONOMIC IMPORTANCE
171
Porphyra yezoensis. Frond shape varies from elliptical to oval or
rounded, with sometimes a cuneate, cordate or even umbilicate basal
region; the margin is undulate and sometimes deeply divided. The
basal part of the frond is blue-green, and the upper reddish-brown.
Kurogi (1961) has outlined in some detail the seasonal life of this
representative. The young fronds are often elongated and elliptical,
tapering at both ends, and becoming more rounded in outline with
increasing age. The fully grown plant can reach a length of 30-60 cm,
and in general only monoecious plants are found. Whilst this is typically a plant of the “ outer ” seas (Kurogi, 1963a) and so found in similar
habitats to those of P. angusta, the growth period of P . yezoensis is
more protracted.
Very young plants appear on “ h i b i ” which are spread in late
September. Where there is an abundance of P . tenera the two plants
appear together on “ h i b i ” spread before the end of October, but
after this the young buds of P . yezoensis appear exclusively, thus
indicating that the period of monospore production by the Conchocelisphase of P . yezoensis is more protracted; in fact this extends into
December. Asexual reproduction by the young buds appears to be
delayed somewhat until after the development of a multiseriate thallus
1-7 om in length. Once this process has started, however, it seems to
continue for the greater part of the growing season. With this plant
asexual reproduction is the only form of multiplication seen in early
autumn, whilst later in autumn and during the winter monosporangia,
carpogonia ” and spermatangia are observed. Some plants show only
asexual organs, and others only “ carpogonia ” and spermatangia.
During spring and summer only the “ sexual ’’ organs are borne on the
newly developed plants. There is thus some degree of overlapping in
the types of spore produced during autumn, winter and spring, but
asexual reproduction is not observed during the summer months.
Plants persist on the “ hibi ” until July, so differing markedly from the
two species already described.
For this species, as with the others so far described, a sexual fusion
is considered to occur in the life-history. Organs associated with this
process first appear in October, frequently on thalli which are still
producing monospores. Areas of the thallus which bear spermatangia
are pale-coloured, and this colour change is first observed in the apical
region, subsequently spreading to the margins. “ Carpogonia ” are
formed in darker coloured parts of the frond below that bearing the
spermatangia, and as the spermatia are released and the “ male
area ” of the frond sloughs away so the “ carpogonial ” areas come in
turn to what is now the upper margin of the frond. Thence vertical
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171
Porphyra yezoensis. Frond shape varies from elliptical to oval or
rounded, with sometimes a cuneate, cordate or even umbilicate basal
region; the margin is undulate and sometimes deeply divided. The
basal part of the frond is blue-green, and the upper reddish-brown.
Kurogi (1961) has outlined in some detail the seasonal life of this
representative. The young fronds are often elongated and elliptical,
tapering at both ends, and becoming more rounded in outline with
increasing age. The fully grown plant can reach a length of 30-60 cm,
and in general only monoecious plants are found. Whilst this is typically a plant of the “ outer ” seas (Kurogi, 1963a) and so found in similar
habitats to those of P. angusta, the growth period of P . yezoensis is
more protracted.
Very young plants appear on “ h i b i ” which are spread in late
September. Where there is an abundance of P . tenera the two plants
appear together on “ h i b i ” spread before the end of October, but
after this the young buds of P . yezoensis appear exclusively, thus
indicating that the period of monospore production by the Conchocelisphase of P . yezoensis is more protracted; in fact this extends into
December. Asexual reproduction by the young buds appears to be
delayed somewhat until after the development of a multiseriate thallus
1-7 om in length. Once this process has started, however, it seems to
continue for the greater part of the growing season. With this plant
asexual reproduction is the only form of multiplication seen in early
autumn, whilst later in autumn and during the winter monosporangia,
carpogonia ” and spermatangia are observed. Some plants show only
asexual organs, and others only “ carpogonia ” and spermatangia.
During spring and summer only the “ sexual ’’ organs are borne on the
newly developed plants. There is thus some degree of overlapping in
the types of spore produced during autumn, winter and spring, but
asexual reproduction is not observed during the summer months.
Plants persist on the “ hibi ” until July, so differing markedly from the
two species already described.
For this species, as with the others so far described, a sexual fusion
is considered to occur in the life-history. Organs associated with this
process first appear in October, frequently on thalli which are still
producing monospores. Areas of the thallus which bear spermatangia
are pale-coloured, and this colour change is first observed in the apical
region, subsequently spreading to the margins. “ Carpogonia ” are
formed in darker coloured parts of the frond below that bearing the
spermatangia, and as the spermatia are released and the “ male
area ” of the frond sloughs away so the “ carpogonial ” areas come in
turn to what is now the upper margin of the frond. Thence vertical
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