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

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Sporelings of both species developed about the same rate.
The ovum, once fertilized, slmll'ly rotates, and moves a short
distance (at least 150-200 Urn) leaving a trail of mucous behind.
~be zygote then begins to swell: in eight hours the dia~meter ~t
D. antarctica oospheres increased from 34.0 ± 0.6 Urn to 46.2 ± 0.2 Urn.
After about 10 hours, a thick wall \.,.ith a sculptured surface forms
a.round the zygol:e. A slight: protuberance then develops, and some
zygotes become sligh tly pear shaped O]'ig. 5,3 ). This protuberance
grows t.o forrn the primary rhizoid p and ultimately a tuft of rhizoids
as depicted in Fig. 5.3 k . After about 24 hours, a septum divides
the zygote into unequal cells, with the smaller cell at tiie rhizoid
end. The larger cell divides transversely again, and the upper
of these two cells then divides longitudinally. After approximately
72 hours, most sporelings WGl"'$ composed o of three or four cells.
Cells derived from the larger initial cell continued to divide, and
form a slightly flattened, oval or obovate body of cells up to
100 )lID long (Fig. 5.3 ). The thick wall tllhich had originally encased
the zygote, is gradually eased off the distal end of this body, and
appears on some sporelings as a "cap" (see Naylor 1953) ,
Cells derived from the smaller initial cell divide less
frequently. The primary rhizoid may be composea of three or four
Cells before i'e begins to show signs of branching (a,t about 9 days).
After a month, two or three rhizoids are formed, and the body of the
sporeling sits upright. The rhizoids interweave so that a mass of
sporelings can be peeled off the glass coverslips. After 6-8 weeks,
the erect portions of the sporelings were 1·-2 mm long and clearly
visible to the naked eye. Despite frequent renewal of the cult.ure
media, the gerrnlings would not develop any further. Nevertheless,
the sporeling at that stage was differentiated into three regions
which conceivably give rise to the lamina, stipe and holdfast.
To obtain further growth. it is probably necessary to transpl~lt Ule
sporeling's to a free flowing seawater system.
(b)
Developmental seguence of D. antarctica and D. wiZlana b~ypnd
General developmental stages of D. anta:t'ctica and D. bn Uana
beyond the sporeling sta,ge are illustrated in Fig. 5.4. 'l'he species
can be separo.t.cd even \Il'hen the plants are quite small (less thEm 5 em
long). D. 1Jril lana stip:::s cue thicke:c, more erect and p:coportionatelv