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

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There is no evidence to suggest that a zygote gives rise to
more than one stipe. A circular holdfast suppor'cing 20 st,ipes
is really an assemblage of 20 plants with their holdfasts fused to form
a composite mass. Since the shape of these composite
resembles that of a holdfast produced by a disc-t'ete plant, the term
"holdfast" has been applied somewhat loosely to botho Ideally, it
should be restricted to the holdfast tissue produced by a single plant.
The term composite holdfast is more appropx-iate where there are several
plan'cs.
Naylor (1949) described the lamina, and stipe of D. antaY'ct'ica as
cOIl1pri sed of a mer is toderm, au ter and inner cortex, and a medulla, in
the sa~e
way that Fritsch (1945:226) described the cellular structure
of certain laminar ian algae. This terminology is followed here,
although I do not consider that it is entirely satisfactory for
reasons outlined bela,.".
In both Naylor's and Fritsch's illustrations~ the meristoderm
is shown to be a surfa.ce layer one cell thick. Naylor (l94,~:
28B) claimed that cell division was confined to this layer, a statement
easily interpreted to mean tha·t all meristematic activity of the
frond is confined to the meristoderm. This is not the case because
cells beneath the meristoderm, i.e. in the outer cortex, also show
signs of mer istema tic acti vi,ty .
Each year, the me ristoderiU I and possibly the cells immediately
beneath, produce a ne\1 layer
the entire surface of the lamina.
5-15 cells thick, which covers
This seals off the ostioles, of
the previous season's conceptacles (see Chapter 6). The surface cells
of this net" layer are slightly smaller and more pigmented than the
cells beneath, and they give rise, in turn the next year, to another
new layer Thus annular bands of cells appecU::- and up to fOtlr
bands can be recognised in some plants (Fig. S. 2d) • The outer two
or three cells of each band stand ou.t as thin bro\·mish lines 0
As mentioned in the next chapter, conceptacles do not seem to
origina.te in the meristoderm. They typically first appear at the
bottom of the uppermost band of cells, and may sometimes form in lONer
bands as well. This indicates that cells beneath the meristoderrn
retain SOme meristematic activity.
Sometimes during the summer, all or part of the surface bC:lDd
of cells may peel off tl1e fronds of both Durvillaea species (Fig. 5.2a,
b,c,e), as thin transparent sheets. Samples examined were about
four cells thick (BO-100 11m). If, as Naylor suggests, growth is