BIOLOGY O F SEAWEEDS OF ECONOMIC IbfPORTANCE
153
insufficient data are available on the precise conditions utilized. Thus
Harries (1932) found that 10 h daily illumination at 1000 lux was
sub-optimal for gametophytes of L. saccharina and Hasegawa (1962)
found 1400 lux sub-optimal for L. angustata, and growth at 5 5006 000 lux at 10°C was greater than in natural light. Gametophytes of
L. angustata matured in 10 days under these conditions. Sundene
(1962) maintained gametophytes of L. digitata at 5°C and in feeble
daylight for indefinite periods without them becoming fertile. Kain
(1963) made a detailed study of light effects on gametophyte growth in
L. hyperborea, in particular keeping a close watch on the irradiance
necessary for gametophyte development (at 10°C). Results showed that
gametophyte development was possible at 26 lux (irradiance = 2.6
pg cal/cm2 sec) using 12 h/day illumination at lO"C, and that the
minimum continuous irradiance was 2 pg cal/cm2 sec ( = 20 lux). The
saturating irradiance for growth was considered to be approximately
between 33-40 pg cal/cm2 (330-400 lux). The results indicate that
growth of the gametophytes is possible at very low levels of light
intensity.
Kain also commented on many earlier references to two types of
female gametophyte, the few celled, early fertile types and the long
filaments which are perennial. High temperatures, enriched media, or
enriched media with low light intensity have been causative factors. A
more critical examination by Kain has shown that gametophytes of
L. hyperborea in the British Isles are produced during autumn and
winter, at a time when there is reduction in available light, lowering of
sea temperature and greater turbidity of the sea. Results show that
spores can survive quite long periods at low light intensity or in the
dark, and that respiratory activity is reduced to a minimum to prevent
excessive use of reserves. Under natural conditions this means an
adequate survival during the winter months, and fairly rapid growth
when conditions improve in the spring. The perennial filamentous
female plants were obtained at higher temperatures in unchanged media,
and low light intensities. Sundene (1962) observed that Laminaria
gametophytes could be cut into fragments, and could still regenerate
cells and be fertile on transference to fresh media.
Various studies have been reported on the nutritional factors
influencing growth of gametophytes (Harries, 1932 ; Carter, 1935).
Walker and Smith (1948) observed that best development of gametophytes of L. hyperborea was obtained in natural sea water enriched
with nitrate, phosphate and bicarbonate, and that addition of uranium
nitrate significantly increased spore development with enhanced rates
of nuclear division, although sporelings died very soon after. Addition
A.M.8.--3
I
153
insufficient data are available on the precise conditions utilized. Thus
Harries (1932) found that 10 h daily illumination at 1000 lux was
sub-optimal for gametophytes of L. saccharina and Hasegawa (1962)
found 1400 lux sub-optimal for L. angustata, and growth at 5 5006 000 lux at 10°C was greater than in natural light. Gametophytes of
L. angustata matured in 10 days under these conditions. Sundene
(1962) maintained gametophytes of L. digitata at 5°C and in feeble
daylight for indefinite periods without them becoming fertile. Kain
(1963) made a detailed study of light effects on gametophyte growth in
L. hyperborea, in particular keeping a close watch on the irradiance
necessary for gametophyte development (at 10°C). Results showed that
gametophyte development was possible at 26 lux (irradiance = 2.6
pg cal/cm2 sec) using 12 h/day illumination at lO"C, and that the
minimum continuous irradiance was 2 pg cal/cm2 sec ( = 20 lux). The
saturating irradiance for growth was considered to be approximately
between 33-40 pg cal/cm2 (330-400 lux). The results indicate that
growth of the gametophytes is possible at very low levels of light
intensity.
Kain also commented on many earlier references to two types of
female gametophyte, the few celled, early fertile types and the long
filaments which are perennial. High temperatures, enriched media, or
enriched media with low light intensity have been causative factors. A
more critical examination by Kain has shown that gametophytes of
L. hyperborea in the British Isles are produced during autumn and
winter, at a time when there is reduction in available light, lowering of
sea temperature and greater turbidity of the sea. Results show that
spores can survive quite long periods at low light intensity or in the
dark, and that respiratory activity is reduced to a minimum to prevent
excessive use of reserves. Under natural conditions this means an
adequate survival during the winter months, and fairly rapid growth
when conditions improve in the spring. The perennial filamentous
female plants were obtained at higher temperatures in unchanged media,
and low light intensities. Sundene (1962) observed that Laminaria
gametophytes could be cut into fragments, and could still regenerate
cells and be fertile on transference to fresh media.
Various studies have been reported on the nutritional factors
influencing growth of gametophytes (Harries, 1932 ; Carter, 1935).
Walker and Smith (1948) observed that best development of gametophytes of L. hyperborea was obtained in natural sea water enriched
with nitrate, phosphate and bicarbonate, and that addition of uranium
nitrate significantly increased spore development with enhanced rates
of nuclear division, although sporelings died very soon after. Addition
A.M.8.--3
I