BIOLOGY OF SEAWEEDS OF ECONOMIC IMPORTANCE
175
occur to a lesser extent. On “ hibi ” spread during late September and
early October, P. tenera and P. angusta are the dominant species, with
some P. kuniedai, P. pseudolinearis and P. yezoensis. “ Hibi ” spread
from mid-October to early November become dominated by P. kuniehi
and P. yezoensis, with some P. tenera mixed. P. yezoensis tends to
dominate on “hibi” spread from November onwards, mixed with
some P. kuniedai, whereas P. kuniedui only is found on nets placed in
the sea during spring and summer. Whilst certain of the species have a
somewhat restricted distribution in the bays where seaweed cultivation
is practised, successful transplants have been made.
Some experiments carried out by Suto (1963) are relevant to the
problems of the Porphyra life-history outlined above, and of importance
to practical seaweed cultivation. I n these experiments some interspecific crossings were attempted with cultivated lavers in order to
obtain new lavers suitable for commercial purposes. Five species were
involved, the dioecious P. pseudolinearis, P. umbilicalis and P. angusta,
and the monoecious P. tenera and P. yezoensks. The formation of the
Conchocelis-phase was taken as evidence that fertilization had been
achieved (see p. 164); according to Suto the contents of an unfertilized “ carpogonium ” either produced spores which again produced
leafy thalli on germination, or the cell contents degenerated. To fully
evaluate the effects of an attempted ‘‘ cross ” between two species, the
full cycle of the life-history was observed. It was claimed that successful crossings were obtained between monoecious species and between
dioecious representatives, but that high mortality rates were obtained
with attempted cross-breeding between monoecious and dioecious
plants. Experiments of this nature involving non-motile reproductive
cells me very difficult to perform, although Sundene (1959) has successfully cross-fertilized different ‘‘ strains ” of Antithamnion plurnulu.
However, full evaluation of these experiments must await demonstration of the cytological changes involved in a fusion of gametes with
Porphyra.
4. Species of Porphyra utilized in the British Isles
Three species of Porphyra are utilized in the British Isles :
Porphyra umbilicalis, P. purpurea and P. lewsticta.
The Conchocelis-phase is produced by all three species, although
that of P. umbilicalis is less readily found. The features of the P.
purpurea life-history which require more adequate verification have
been indicated (Conway, 1964a, b, c).
Whilst in the British Isles the Porphyra species which are utilized
175
occur to a lesser extent. On “ hibi ” spread during late September and
early October, P. tenera and P. angusta are the dominant species, with
some P. kuniedai, P. pseudolinearis and P. yezoensis. “ Hibi ” spread
from mid-October to early November become dominated by P. kuniehi
and P. yezoensis, with some P. tenera mixed. P. yezoensis tends to
dominate on “hibi” spread from November onwards, mixed with
some P. kuniedai, whereas P. kuniedui only is found on nets placed in
the sea during spring and summer. Whilst certain of the species have a
somewhat restricted distribution in the bays where seaweed cultivation
is practised, successful transplants have been made.
Some experiments carried out by Suto (1963) are relevant to the
problems of the Porphyra life-history outlined above, and of importance
to practical seaweed cultivation. I n these experiments some interspecific crossings were attempted with cultivated lavers in order to
obtain new lavers suitable for commercial purposes. Five species were
involved, the dioecious P. pseudolinearis, P. umbilicalis and P. angusta,
and the monoecious P. tenera and P. yezoensks. The formation of the
Conchocelis-phase was taken as evidence that fertilization had been
achieved (see p. 164); according to Suto the contents of an unfertilized “ carpogonium ” either produced spores which again produced
leafy thalli on germination, or the cell contents degenerated. To fully
evaluate the effects of an attempted ‘‘ cross ” between two species, the
full cycle of the life-history was observed. It was claimed that successful crossings were obtained between monoecious species and between
dioecious representatives, but that high mortality rates were obtained
with attempted cross-breeding between monoecious and dioecious
plants. Experiments of this nature involving non-motile reproductive
cells me very difficult to perform, although Sundene (1959) has successfully cross-fertilized different ‘‘ strains ” of Antithamnion plurnulu.
However, full evaluation of these experiments must await demonstration of the cytological changes involved in a fusion of gametes with
Porphyra.
4. Species of Porphyra utilized in the British Isles
Three species of Porphyra are utilized in the British Isles :
Porphyra umbilicalis, P. purpurea and P. lewsticta.
The Conchocelis-phase is produced by all three species, although
that of P. umbilicalis is less readily found. The features of the P.
purpurea life-history which require more adequate verification have
been indicated (Conway, 1964a, b, c).
Whilst in the British Isles the Porphyra species which are utilized