AFFINITIES AND CLASSIFICATION OF ALG X. 57 
would appear to be a necessary condition of life for the greater 
part of the inhabitants of deep seas, and indeed of salt water 
generally. In the huge group of Phwospores we have every 
grade of transition from isogamous to heterogamous reproduc- 
tion; and, if the principle of classification based solely on the 
mode of reproduction were consistently carried out, a part of 
this obviously natural group must be placed in the Zygophycese, 
a part in the Oophyce®, with other forms intermediate between 
the two; and in some cases even members of the same family 
would be separated. The typical Pheosporem, suchas Punctaria 
and Sporochnus, are characterized by the possession of two kinds 
of zoosporange, unilocular and multilocular. The zoospores pro- 
duced in the two kinds of sporange present no difference in size 
or form; but those from the unilocular sporanges appear in all 
cases to germinate directly, while those from the multilocular 
sporanges are sometimes zoogametes with sexual functions. In 
some families one or other kind of zoosporange is altogether 
suppressed; thus the Laminariaces * have the unilocular kind 
only. In the Hetocarpacee and a few other genera scattered 
through different families, we have a mode of reproduction closely 
resembling that in the isogamous Confervoidee, except in the 
greater differentiation of the zoosporanges—a conjugation of 
zoogametes (from the multilocular sporanges) which are to all 
appearance exactly alike, though a slight differentiation is exhi- 
bited in the fact of one of them coming to rest and partially 
losing its cilia before conjugation takes place. In the Outleriacee 
the differentiation is more complete; the male and female swarm- 
cells are produced either on the same or on different individuals ; 
the latter are much larger than the former, and come perfectly to 
rest, entirely losing their cilia before being impregnated by the 
former. In the Dictyotee, finally, the differentiation is carried 
still further, and the female reproductive bodies are, from the 
first, motionless masses of protoplasm not provided with cilia 
(oospheres) The Dictyotew are further distinguished from the 
other Phæosporeæ in the non-motile character of both the male 
and the non-sexual reproductive elements; and in these respects 
they present a singular identity of structure with the Florideæ. 
In Dictyosiphon a different mode of reproduction has been 
observed, somewhat resembling the conjugation of the Conjugatæ. 
* Gardiner believes, however, that he has detected a true sexual reproduc- 
tion in Alaria. ` 
LINN. JOURN.— BOTANY, VOL. XXIV. F 
