18 MARCUS M. HARTOG. 
indicating the formation of the gametes by a binary fission of 
potential zoospores. 
The SirpHone# form continuous apocytia, parts of which may 
become partitioned off as gametangia. 
ACETABULARIA and BotrypiumM 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,! 
and must become plurinucleate before being resolved into the 
gametes. Inthat of Acetabularia the protoplasm surrounds 
a central vacuole, and the cytoplasm immediately round this 
persists without taking any part in the gametoparous segmen- 
tation, but serves by its turgescence to liberate the gametes. 
These are exogamous, andin Acetabularia may form multiple 
unions—two to six.” 
Bryoprsis is anisogamous. Here gametangia are cut off, 
males and females being on distinct plants. According to 
Berthold, repeated bipartitions of the nuclei precede the reso- 
lution 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. 
Dasyciapvus 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 pro- 
cess 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 pre- 
liminary mitosis or “excretion” expresses no universal law. 
We have adverted above to the peculiarly strong exogamy 
of this genus. 
In Derpesia it is stated’ that no sexual process is known ; 
1 Of Rostafinsky, in ‘ Bot. Zeit.,’ 1877. 
? If the gametogonia be kept long in a resting state, the bodies they pro- 
duce behave like ordinary zoospores, and will not conjugate. 
® Welle, in ‘ Engler and Prantl,’ op. cit., i, § 2, p. 129. 
