PH.ffiOSPOKE.iE; FUCACEjE 



627 



sporanges appear in all cases to germinate directly, while those from 

 the multilocular sporanges sometimes coalesce in pairs before ger- 

 minating. The different families of Phceosporece present a most 

 interesting gradual transition from the conjugation of swarm-cells 

 to the impregnation of a female * ob'sphere ' by male antherozoids. 

 In Ectocarpus, Giraudia, and Scytosiphon, conjugation takes place 

 between swarm-cells from the multilocular sporanges which appear 

 to be exactly alike, but a slight differentiation is exhibited in one of 

 them coming to rest and partially losing its cilia before conjugation 

 takes place (fig. 469, II). Malfe Asexual organs also occur in the 

 Sphacelariacece, but no actual process of conjugation has as yet been 

 observed. In Cutleria and Zaiiar- 

 dinia 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 Dictyota the differentiation is 

 ( -ariied still further, and the 

 female reproductive bodies are true 

 ' obspheres/ being from the first 

 motionless masses of protoplasm not 

 provided with cilia, while the an- 

 therozoids exhibit motility only for 

 a very short time, and each is pro- 

 vided only with a single cilium of 

 unusual length. In the family 

 Laminar iacece, belonging to the 

 Phceosporece, are included many of 

 the largest of the seaweeds, chiefly 

 natives of southern seas, the frond 

 often attaining enormous dimen- 

 sions, and exhibiting rudimentary 

 differentiation into rhizoids or 

 organs of attachment, stem, and 

 leaves. Such are Lessonia, which 

 grows to a great height and re- 

 sembles a branching tree with pendent leaves two or three feet 

 long ; Macrocystis, where the stalk like base of each branch of the 

 leaf is hollowed out into a large pear-shaped air-bladder ; Nereocystis, 

 Laminaria, and others. 



In the Fucaceae the generative apparatus is contained in the 

 globular ' conceptacles/ which are usually sunk in the tissue near the 

 extremities of the fronds. In some species, as Fucus platycarpus, 

 the same conceptacles contain both * antherids ' and l obgones ; ' in 

 others these two sexual elements are disposed in different conceptacles 

 on the same plant ; whilst in the commonest of all, F. vesiculosus 

 (bladder- wrack), they are limited to different individuals. When a 



s s 2 



FIG. 469. Process of conjugation 

 in Ectocarpus silicnlosus. (From 

 Vines's ' Physiology.') I. a-/, the 

 female zobspore coming to rest ; 

 II., the female zoospore at rest, 

 surrounded by male zoospores ; 

 III. a-e, fusion of male and female 

 zoospores. 



