Some Problems of Reproduction: a Comparative Study of ...

18 MARCUS M. HARTOG.
indicating the formation of the gametes by a binary fission of
potential zoospores.
The SIPHONED form continuous apocytia, parts of which may
become partitioned off as gametangia.
ACETABULARIA and BOTBYDITTM are exo-isogamous; their
gametes are formed in gametogonia, which are formed by the
resolution of an apocytium into cells, and have the character
of resting spores. The gametogonium is at first uninucleate,
at least in Botrydium, judging from the original figure, 1
and must become plurinucleate before being resolved into the
gametes. In that of Acetabularia the protoplasm surrounds
a central vacuole, and the cytoplasm immediately round this
persists without taking any part in the gametoparous segmentation,
but serves by its turgescence to liberate the gametes.
These are exogamous, and in Acetabularia may form multiple
unions—two to six. 2
BRYOPSIS is anisogamous. Here gametangia are cut off,
males and females being on distinct plants. According to
Berthold, repeated bipartitions of the nuclei precede the resolution
into gametes. There is a formation of epiplasm between
the gametes, as in Cladophora, besides a central bladder, as in
Acetabularia. The reproductive organs of Codium appear
to be similar in most respects.
DASYCLADUS forms its gametes also by the resolution of an
apocytial gametangium into cells ; but here a fusion of several
vegetative nuclei constitutes each single gametonucleus, a process
of which we shall find other instances in this group. We
now learn that the view that a gametonucleus or pronucleus
differs from an ordinary one in being reduced either by preliminary
mitosis or " excretion" expresses no universal law.
We have adverted above to the peculiarly strong exogamy
of this genus.
In DERBESIA it is stated 8 that no sexual process is known;
1
Of Rostafinsky, in ' Bot. Zeit.,' 1877.
s
If the gametogonia be kept long in a resting state, the bodies they produce
behave like ordinary zoospores, and will not conjugate.
a
Welle, in ' Engler and Prantl,' op. cit., i, § 2, p. 129.