A biological study of Durvillaea antarctica (Chamisso) Hariot and D ...

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D. wilZana:
Apart from obvious differences like the total absence of any
honeycomb tissue, and the production of lateral laminae, the growth
pattern of D. willana differs from D. antarctica in that its rate
of stipe elongation does not decline as abrupt.ly once plants are
005-1.0 111 long. At a given locality, almost all D. willana stipes
are proportionB.tely longer than those of D. ' antarctica.
(~"here
At 'f'autuku
the total length a'ctained by both species is about the same)
2 m D. willana stipes are cO!J1.\l1on, whereas the longest D. antarctica
stipe recorded in the area was only 0.6 m. Thus the "stipe fraction"
of plant wet weight does not decline as markedly for D. willana as
plants grow. For plants 0.75-1.0 m (n~94) and longer than 5 m
(n:::::53) stipes formed 31,1% and 23% respectively of plantwe·lght:.
Subsequent development of D. willana is characterised by the
formation of lateral laminae. Small pimple-like processes appear
on the stipe, usually first at the distal end, and then gradually at
lower levels. These become stipitate lateral laminae, some of
1l1hich may be as large as the primary lamina" The presence or absence
of the primary lamina determines the degree of development of tIle
laterals. Both the primary lamina and lateral laminae can form
additional stipitate laterals adventitiously (Fig. S.Sb)G These
usually arise along the lower margins but are occasionally seen
growing from the plane surface.
The primary and lateral laminae are also usually divided into
thongs of varying v!idth, although they do not become as narrowly
divided as some D. antarctica laminae.
laminae are more extensively perforated.
In general, la:r.:ge D. wi llana
In both species, division of the lamina is partly caused by the
formation of small holes. Naylor (1953:295) establi.shed that these
were not simply caused by injuries to the lamina tissue; they originate
as small splits in the lamina, and the positions of these appear to
be predetermined in the cortex. An incipient split can often be
recognised as a faint brown line. The splits grow to form small
round holes which enlarge and elongate to an extent that the lamina.
is divided. The factor (g) responsilile for the forma-tion of these
holes are not known l although small specimens grox-Jing in areas of
strong wave action have more highly perforated fronds than others
growing in semi--sheltered localities." It seems that either di:cec'Uy
or indirectly. wave cction is an important cause,