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A. D. BONEY
12 months in age, and the younger the plant the more readily it recovers after cutting (or tearing) of the fronds. This is probably because
of the more intensive meristematic activity of the base of the frond.
Regenerative growth is possible as long as some 15-20 cm of the frond
is left,-complete removal results in a rotting away of the stipe.
Change in frond width during the growth phase is reflected in the shape
of the base of the lamina, being fusiform in rapid growth, changing to
cuneate and to sub-cordate with successive slowing down of the growth
rate. Frond width is also greatest during the second rapid growth
phase. A regular defoliation of lamina tissue from the apex is observed,
shown more regularly by plants in sublittoral habitats than in intertidal habitats where environmental conditions may supervene. In
sublittoral habitats tissue formed in the first 6 months of the year is
cast in the second half, and the tissue formed between July and December is cast in the next 6 months.
Stipe and holdfast growth is also rhythmic in pattern. Growth in
length and thickness of the stipe is more rapid between January and
June than from July to December. As the rate of stipe growth increases
in the apical region the formation of a new series of haptera is observed
at the base of the stipe. Increase in girth of the stipe is accompanied
by formation of a secondary meristem, and the first activity of this is
seen at the base of the stipe. The seasonal change in stipe growth may
be seen in the alternate zones of lighter and darker tissue, the darker
(small-celled) tissue being formed during the periods of slow growth.
Reproductive tissues develop in the plants 8-12 months old, and
plants which start developing in the fast growth period mature more
rapidly than those which commence growth later in the year. For the
sporangium development to commence, the distal tissue of the frond
must be at least 6 months old. Once initiated, sporangia mature in
14-21 days and may continue to liberate zoospores for 2-3 months.
Ripe sporangia number some 1 000 000/cm2 at first, falling to 500 OOO/
cm2 of frond surface after 14 days and the greater number of zoospores
are released during the first few weeks of reproductive activity. Thirtytwo zoospores are produced per sporangium, and estimates show that
1 cm2 of frond surface can produce 64000000 spores over a 3-month
period. Despite this vast potential, the time over which spore production can take place will depend upon the degree of survival of the plant,
or of the frond tissue, in a particular habitat. Maximum production of
reproductive tissue is observed in a 2nd-year plant. During the year,
the main period of formation of reproductive tissue is observed between October and March, particularly with frond tissue developed
from April to September. Whilst there will be variations in the time
A. D. BONEY
12 months in age, and the younger the plant the more readily it recovers after cutting (or tearing) of the fronds. This is probably because
of the more intensive meristematic activity of the base of the frond.
Regenerative growth is possible as long as some 15-20 cm of the frond
is left,-complete removal results in a rotting away of the stipe.
Change in frond width during the growth phase is reflected in the shape
of the base of the lamina, being fusiform in rapid growth, changing to
cuneate and to sub-cordate with successive slowing down of the growth
rate. Frond width is also greatest during the second rapid growth
phase. A regular defoliation of lamina tissue from the apex is observed,
shown more regularly by plants in sublittoral habitats than in intertidal habitats where environmental conditions may supervene. In
sublittoral habitats tissue formed in the first 6 months of the year is
cast in the second half, and the tissue formed between July and December is cast in the next 6 months.
Stipe and holdfast growth is also rhythmic in pattern. Growth in
length and thickness of the stipe is more rapid between January and
June than from July to December. As the rate of stipe growth increases
in the apical region the formation of a new series of haptera is observed
at the base of the stipe. Increase in girth of the stipe is accompanied
by formation of a secondary meristem, and the first activity of this is
seen at the base of the stipe. The seasonal change in stipe growth may
be seen in the alternate zones of lighter and darker tissue, the darker
(small-celled) tissue being formed during the periods of slow growth.
Reproductive tissues develop in the plants 8-12 months old, and
plants which start developing in the fast growth period mature more
rapidly than those which commence growth later in the year. For the
sporangium development to commence, the distal tissue of the frond
must be at least 6 months old. Once initiated, sporangia mature in
14-21 days and may continue to liberate zoospores for 2-3 months.
Ripe sporangia number some 1 000 000/cm2 at first, falling to 500 OOO/
cm2 of frond surface after 14 days and the greater number of zoospores
are released during the first few weeks of reproductive activity. Thirtytwo zoospores are produced per sporangium, and estimates show that
1 cm2 of frond surface can produce 64000000 spores over a 3-month
period. Despite this vast potential, the time over which spore production can take place will depend upon the degree of survival of the plant,
or of the frond tissue, in a particular habitat. Maximum production of
reproductive tissue is observed in a 2nd-year plant. During the year,
the main period of formation of reproductive tissue is observed between October and March, particularly with frond tissue developed
from April to September. Whilst there will be variations in the time