BIOLOGY OF SEAWEEDS OF ECONOMIC IMPORTANCE
161
Laminaria (p. 153). The newly attached zoospores, gametophytes and
the young sporophytes of U . pinnatijda survive protracted periods of
exposure to air of 100% R.H., whereas at 70% R.H. zoospores are
killed within 30 min and the young gametophytes and sporophytes in
1-3 h. At higher temperatures the period of tolerance is reduced
(Saito, 1960a). The form range of Undaria pinnatijda has also been
studied (Saito, 1960b ; Kato and Nakahisa, 1962). Of the three principal forms described (f. typica, f. distans, f. narutensis), biometrical
measurements of the main diagnostic characters and growth of the
sporophytes under identical conditions from gametophytes collected
from a number of widely separated localities showed that the different
characters (frond and stipe length, frond shape, relationship between
blade and sporophyll, condition of sporophyll surface) were mainly
hereditary, and were not changed under conditions of culture or in
changed habitats.
The periodicity of zoospore shedding has also been studied with
Undaria sporophylls (Suto, 1952). Release of spores commences when
the sea temperature reaches 14°C (i.e. during spring). Spores are
released in vast quantities a t 2-hourly intervals between 9 a.m. and
6 p.m., and on every 4-6 days enormous numbers are released. Light
or dark periods seem to have little effect on spore release. Previous
drying of the sporophylls prior to immersion hastens the onset of zoospore release, but has no effect on the numbers obtained.
Undaria plants grow best in sublittoral habitats (depth 20 to 40 ft)
where there is a strong current action. The blades are harvested
between February and June by means of long-handled rakes (Chapman,
1950).
11. Alaria
Although used to a smaller extent than the other genera so far
described, detailed studies on some aspects of the biology of certain
Alaria species have been reported in recent years: Sundene (1961)
described the results of some interesting experimental work carried out
with Ahria esculenta in Norway. For example, in transplant experiments where plants were moved during autumn from the west coast to
Oslofjord, whilst the test plants reattached themselves successfully to
the new substrata, they died and disappeared in late summer and early
autumn. And whilst the transplanted material became fertile in the
winter months and produced young plants in the vicinity, none of the
young plants survived the summer. Experimental studies on the male
and female gametophytes showed that they were able to survive long
periods in culture medium at low levels of light intensity, and with
I*
161
Laminaria (p. 153). The newly attached zoospores, gametophytes and
the young sporophytes of U . pinnatijda survive protracted periods of
exposure to air of 100% R.H., whereas at 70% R.H. zoospores are
killed within 30 min and the young gametophytes and sporophytes in
1-3 h. At higher temperatures the period of tolerance is reduced
(Saito, 1960a). The form range of Undaria pinnatijda has also been
studied (Saito, 1960b ; Kato and Nakahisa, 1962). Of the three principal forms described (f. typica, f. distans, f. narutensis), biometrical
measurements of the main diagnostic characters and growth of the
sporophytes under identical conditions from gametophytes collected
from a number of widely separated localities showed that the different
characters (frond and stipe length, frond shape, relationship between
blade and sporophyll, condition of sporophyll surface) were mainly
hereditary, and were not changed under conditions of culture or in
changed habitats.
The periodicity of zoospore shedding has also been studied with
Undaria sporophylls (Suto, 1952). Release of spores commences when
the sea temperature reaches 14°C (i.e. during spring). Spores are
released in vast quantities a t 2-hourly intervals between 9 a.m. and
6 p.m., and on every 4-6 days enormous numbers are released. Light
or dark periods seem to have little effect on spore release. Previous
drying of the sporophylls prior to immersion hastens the onset of zoospore release, but has no effect on the numbers obtained.
Undaria plants grow best in sublittoral habitats (depth 20 to 40 ft)
where there is a strong current action. The blades are harvested
between February and June by means of long-handled rakes (Chapman,
1950).
11. Alaria
Although used to a smaller extent than the other genera so far
described, detailed studies on some aspects of the biology of certain
Alaria species have been reported in recent years: Sundene (1961)
described the results of some interesting experimental work carried out
with Ahria esculenta in Norway. For example, in transplant experiments where plants were moved during autumn from the west coast to
Oslofjord, whilst the test plants reattached themselves successfully to
the new substrata, they died and disappeared in late summer and early
autumn. And whilst the transplanted material became fertile in the
winter months and produced young plants in the vicinity, none of the
young plants survived the summer. Experimental studies on the male
and female gametophytes showed that they were able to survive long
periods in culture medium at low levels of light intensity, and with
I*