168
A. D. BONEY
L. longicuris carried out by MacFarlane (1952a) showed that of 200
marked plants, fifteen per cent of L. digitata and three and one quarter
per cent of L. longicuris survived a 9-month period (October-July).
Laminaria hyperborea. The growth of plants of L. hyperborea
follows a similar course to that of L. saccharina, showing annual phases
of fast and slow growth, and primary and secondary growth in stipe and
frond. In analyses of several populations (Kain, 1963) plants up to 13
years old have been found, but the bulk of the population usually lies
between 1-4 years. The density of the sublittoral population appears to
be fairly constant down to the lower limit of density of the population,
although this lower limit will vary with the type of habitat. Larger
plants of 6 years or more of age are more selectively destroyed by some
environmental factor. The period of fast growth commences in winter,
and initial growth of the frond takes place at the expense of reserves
stored in the stipe. These reserves are then built-up again when there
are more suitable light conditions. Fronds and stipes have similar
fresh weights in April. This increase in fresh weight will result mainly
from assimilatory activity. Observations made within the limited
latitude range of the British Isles showed that conditions for the
growth of Laminaria plants were more favourable in the northerly
latitudes (Scotland), and large plants of an older age grouping were to be
found there.
Tramplantation experiments with Laminaria. Different forms of
Laminaria digitata are known in Norway, (e.g. f. stenophylla, f. genuina,
and f. typica), and these have been found interfertile (Sundene, 1968).
Hybrids between these various forms and " true " forms were successfully reared in culture up to 1-2 cm in length and then " transplanted "
by careful attachment to floating rafts in the sea. Change in environmental conditions had marked effects on the form of frond. Thus the
fronds of plants in sheltered habitats retain an elongate, undivided
habit, whereas those exposed to severe wave action become broader
and much divided.
Transplantation experiments showed that the most favourable time
was in early autumn when sea temperatures were below 15"C, and plants
placed in the sea at this, time attained a greater length than those
transferred during the winter months. The summer months were
observed to be the most critical during which loss of plants was greatest
with noticeable decrease in length of the fronds in many instances.
Growth of the fronds was also markedly reduced during the summer
months. Growth rates then picked up again during the autumn and
A. D. BONEY
L. longicuris carried out by MacFarlane (1952a) showed that of 200
marked plants, fifteen per cent of L. digitata and three and one quarter
per cent of L. longicuris survived a 9-month period (October-July).
Laminaria hyperborea. The growth of plants of L. hyperborea
follows a similar course to that of L. saccharina, showing annual phases
of fast and slow growth, and primary and secondary growth in stipe and
frond. In analyses of several populations (Kain, 1963) plants up to 13
years old have been found, but the bulk of the population usually lies
between 1-4 years. The density of the sublittoral population appears to
be fairly constant down to the lower limit of density of the population,
although this lower limit will vary with the type of habitat. Larger
plants of 6 years or more of age are more selectively destroyed by some
environmental factor. The period of fast growth commences in winter,
and initial growth of the frond takes place at the expense of reserves
stored in the stipe. These reserves are then built-up again when there
are more suitable light conditions. Fronds and stipes have similar
fresh weights in April. This increase in fresh weight will result mainly
from assimilatory activity. Observations made within the limited
latitude range of the British Isles showed that conditions for the
growth of Laminaria plants were more favourable in the northerly
latitudes (Scotland), and large plants of an older age grouping were to be
found there.
Tramplantation experiments with Laminaria. Different forms of
Laminaria digitata are known in Norway, (e.g. f. stenophylla, f. genuina,
and f. typica), and these have been found interfertile (Sundene, 1968).
Hybrids between these various forms and " true " forms were successfully reared in culture up to 1-2 cm in length and then " transplanted "
by careful attachment to floating rafts in the sea. Change in environmental conditions had marked effects on the form of frond. Thus the
fronds of plants in sheltered habitats retain an elongate, undivided
habit, whereas those exposed to severe wave action become broader
and much divided.
Transplantation experiments showed that the most favourable time
was in early autumn when sea temperatures were below 15"C, and plants
placed in the sea at this, time attained a greater length than those
transferred during the winter months. The summer months were
observed to be the most critical during which loss of plants was greatest
with noticeable decrease in length of the fronds in many instances.
Growth of the fronds was also markedly reduced during the summer
months. Growth rates then picked up again during the autumn and