BIOLOGY OF SEAWEEDS OF ECONOMIC IMPORTANCE
141
early summer, but a rapid fall in value later in the summer due to
maturation of fruiting receptacles formed in the course of the 2nd year.
In autumn the dry weights started to pick up again, but fell off in
December. With short-day conditions and sea temperatures remaining fairly high this was probably due to an excess of respiration over
assimilation. Increase in dry weight was a cumulative process with
growing branches.
The production of fertile receptacles and release of gametes is of
importance not only because of the recruitment of young plants, but
also because of the metabolic changes involved. The effects on the
growth rate of branches has been mentioned above. In the British
Isles the first indications of receptacle formation are to be seen in May
and June, and conceptacle formation is first observed in the autumn
(David, 1943). With approaching maturity of the conceptacles the
receptacles increase in volume, and the most marked increase in size
is from February to May. After May dehiscence of the receptacles and
discharge of their contents is observed. There is evidence that on
southern shores of the British Isles the phasing of this process is timed
a little earlier in the year than on more northern shores. Similarly
David showed that dehiscence and release of gametes occurs earlier
with plants growing near the upper limits of the Ascophyllum zone.
Studies in the fruiting of Ascophyllurn on the coast of Norway have been
reported by Printz ( 1 9 5 6 ~ ~
1959a), with plants selected from localities
at different latitudes. Maturation of the receptacles occurs during
April in Southern Norway, whereas on northern shores this is later
by 40-45 days. However, whilst various phases of the growth of Ascophyllum plants in Northern Norway lag noticeably behind those of
plants on southern shores during winter, spring and early summer, this
gap is reduced considerably during the rest of the summer when the
northern plants show a marked increase in the rates of growth, and in
some instances may overtake the southern plants. The retardation
due to lowered temperatures and much shortened day length in the
north during the winter is then largely made up. Whilst the period of
fruiting may be a protracted one, reports on the growth of very young
Ascophyllum plants are sparse, and David (1943) found very few specimens in the Ascophyllum zone (Fig. 6).
Harvesting of Ascophyllum must clearly be linked with both the
growth and reproductive phases in the life history, but since there are
indications that sporeling growth is not very prolific, both longevity of
the plants and frond growth after cutting need to be assessed. Estimates of the age of the plants are made easier by the annual production
of vesicles. David (1943) estimated the mean age of plants in the middle
141
early summer, but a rapid fall in value later in the summer due to
maturation of fruiting receptacles formed in the course of the 2nd year.
In autumn the dry weights started to pick up again, but fell off in
December. With short-day conditions and sea temperatures remaining fairly high this was probably due to an excess of respiration over
assimilation. Increase in dry weight was a cumulative process with
growing branches.
The production of fertile receptacles and release of gametes is of
importance not only because of the recruitment of young plants, but
also because of the metabolic changes involved. The effects on the
growth rate of branches has been mentioned above. In the British
Isles the first indications of receptacle formation are to be seen in May
and June, and conceptacle formation is first observed in the autumn
(David, 1943). With approaching maturity of the conceptacles the
receptacles increase in volume, and the most marked increase in size
is from February to May. After May dehiscence of the receptacles and
discharge of their contents is observed. There is evidence that on
southern shores of the British Isles the phasing of this process is timed
a little earlier in the year than on more northern shores. Similarly
David showed that dehiscence and release of gametes occurs earlier
with plants growing near the upper limits of the Ascophyllum zone.
Studies in the fruiting of Ascophyllurn on the coast of Norway have been
reported by Printz ( 1 9 5 6 ~ ~
1959a), with plants selected from localities
at different latitudes. Maturation of the receptacles occurs during
April in Southern Norway, whereas on northern shores this is later
by 40-45 days. However, whilst various phases of the growth of Ascophyllum plants in Northern Norway lag noticeably behind those of
plants on southern shores during winter, spring and early summer, this
gap is reduced considerably during the rest of the summer when the
northern plants show a marked increase in the rates of growth, and in
some instances may overtake the southern plants. The retardation
due to lowered temperatures and much shortened day length in the
north during the winter is then largely made up. Whilst the period of
fruiting may be a protracted one, reports on the growth of very young
Ascophyllum plants are sparse, and David (1943) found very few specimens in the Ascophyllum zone (Fig. 6).
Harvesting of Ascophyllum must clearly be linked with both the
growth and reproductive phases in the life history, but since there are
indications that sporeling growth is not very prolific, both longevity of
the plants and frond growth after cutting need to be assessed. Estimates of the age of the plants are made easier by the annual production
of vesicles. David (1943) estimated the mean age of plants in the middle