136
A. D. BONEY
shore region, competing with Asmphyllum in some localities, and
replacing it in others where there is exposure to more severe wave
action. Irrespective of the time of settlement of the oospore, growth in
length is a relatively uniform process. Mean growth rates (linear extension) were found to equal 0.45-0.48 cm/week on the Devon and Manx
coasts. On sheltered shores in Scotland the rate was 0.68 cmlweek, and
on shores exposed to severe wave action 0.31 cmlweek. Slower growth
rates than this have been observed on the Norwegian coast (Printz,
1926). Very long plants appear to develop where there is a marked
lowering of salinity.
The morphological rhythm of frond development over the seasons
shows a clear-cut pattern. Successive dichotomies of the apical cells
results in a division of the plant into sections, called " internodes ".
The internode will further extend in length after branching. The
dichotomy/length relationship is available for different parts of the
geographical range of the plant; for instance plants in the Isle of Man
showed a greater degree of forking (i.e. more dichotomies per length)
than those on the Devon coast, and on Scottish shores exposed to severe
wave action it was considerably greater. The division of the apical cell
appears not to be a true dichotomy, since the growth potential of one
arm of the branching is greater than the other, and in fact the growth
appears to be more monopodial than dichotomous. Usually the arm
with the lower growth potential forms reproductive branches. As the
plant ages so the basal region consists mainly of the midrib portion with
spur-like branch remnants. Vesicle formation is observed in the spring,
and with young plants a minimum length must be reached before
vesicles are formed (10-14 cm). The degree of vesiculation varies with
habitat; vesicles are lacking on plants exposed to very severe wave
action. I n Norway vesicle formation and branch growth commences
earlier on southern shores than in more northern latitudes, but (as
for Ascophyllum, p. 141) the summer growth of plants in the north
rapidly catches up with and passes that of plants in the south, with the
result that conceptacle development is initiated in early autumn in the
north, whilst in the south this phase is not reached until a further six
weeks have passed. Further development in the northern plants is
suppressed during the winter months, with the result that the conceptacles of the southern plants mature and release their oogonia earlier
in the following year than those of plants in the north (Printz,
Fwus serratus grows in a lower zone on the shore than Fwus
vesiculosus. Growth in length on the Devon coast shows a mean value
of 0.49 cmlweek. On the coast of the Isle of Man the rate varied
19598).
A. D. BONEY
shore region, competing with Asmphyllum in some localities, and
replacing it in others where there is exposure to more severe wave
action. Irrespective of the time of settlement of the oospore, growth in
length is a relatively uniform process. Mean growth rates (linear extension) were found to equal 0.45-0.48 cm/week on the Devon and Manx
coasts. On sheltered shores in Scotland the rate was 0.68 cmlweek, and
on shores exposed to severe wave action 0.31 cmlweek. Slower growth
rates than this have been observed on the Norwegian coast (Printz,
1926). Very long plants appear to develop where there is a marked
lowering of salinity.
The morphological rhythm of frond development over the seasons
shows a clear-cut pattern. Successive dichotomies of the apical cells
results in a division of the plant into sections, called " internodes ".
The internode will further extend in length after branching. The
dichotomy/length relationship is available for different parts of the
geographical range of the plant; for instance plants in the Isle of Man
showed a greater degree of forking (i.e. more dichotomies per length)
than those on the Devon coast, and on Scottish shores exposed to severe
wave action it was considerably greater. The division of the apical cell
appears not to be a true dichotomy, since the growth potential of one
arm of the branching is greater than the other, and in fact the growth
appears to be more monopodial than dichotomous. Usually the arm
with the lower growth potential forms reproductive branches. As the
plant ages so the basal region consists mainly of the midrib portion with
spur-like branch remnants. Vesicle formation is observed in the spring,
and with young plants a minimum length must be reached before
vesicles are formed (10-14 cm). The degree of vesiculation varies with
habitat; vesicles are lacking on plants exposed to very severe wave
action. I n Norway vesicle formation and branch growth commences
earlier on southern shores than in more northern latitudes, but (as
for Ascophyllum, p. 141) the summer growth of plants in the north
rapidly catches up with and passes that of plants in the south, with the
result that conceptacle development is initiated in early autumn in the
north, whilst in the south this phase is not reached until a further six
weeks have passed. Further development in the northern plants is
suppressed during the winter months, with the result that the conceptacles of the southern plants mature and release their oogonia earlier
in the following year than those of plants in the north (Printz,
Fwus serratus grows in a lower zone on the shore than Fwus
vesiculosus. Growth in length on the Devon coast shows a mean value
of 0.49 cmlweek. On the coast of the Isle of Man the rate varied
19598).