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

29
(i)
Hol,dfast
The external morphology of holdfas'cs is not a
reliable means of sepaL'i'lting the species.
Holdfasts of all species
are capable of g:cafting to one another to form composite holdfasts
supporting several stipes (Chaptez- S), but this phenomenon is much
more common with one species than with the rest
It is
that some holdfasts are excavated by biJrrowing animals and are full
of holes, while. ol~hers are never excavated and from holes"
Depending on the species, the of a1~t.a.ch\Oen't of Lhe ,... j:ipe may be
recessed, into the holdfas't r O.t" th ere may be no rece ss ,
y
t
(ii) Stipe
Stipas of all species are roughly oval or circular at the base.
'l"hey taper distally and become slightly flattened immediately below
the lamina. stipe size varies with ,wave action, with latitude and
according to the level that the plant grows on the shore (South and
Hay 1977), but is nevertheless an important: cr:i'terion for
'the species e
The transition from stipe to lamina is more abrupt in some species
tJ)an in others; and the pr~sence of o. shallow fULt'OW running pa.:ct way
down the stipe from its distal end is worth noting'. So too is the
occurrence of any dist.al branching in'co seve:t:al thickened, bough--like
processes .... yhich, give rise to major. divisions of the lamina (Fig. 5.11
il,b) .
The presence or absence of lateral blades, or even
small bud-like processes along the stipe is a very nseh)'l feature
to separate the species. ~rhe surface may be unifo:cmly smooth I or
there may be distinct gJ:ooves around the stipe. 'f'hese gr.-ooves (1-3 mm,
wide) Here described in some detail by lle["cioLt (1923) who rather
inappropriately refel:red to them as pi'c,s.. wJ!efl presen-l:, they cH'P'
localised at the base of the stipe or Cl,t the end. They are
bounded by a thick layer of outer cortical cells, ~1nd
enhance the flexibility of the
iSI.ppeal: t~o
( iii) £amina
Ec.u::lier workex:s used laminc\ colour' to differenti2t,te between
species, but: t.his character is quite IJnf.'Gliable when
isolo,ted- 'J'he v",ria tion Is colOlJJ:' '.vi thin ;1 specie:~ is
as any variation between Plants J.n
sel1lisheltered locc>.lities or on the sho):'e are