FUCUS. 



[ 277 ] 



FUCUS. 



eiied clubs, on which, by the naked eye, may 

 be distinguished a number of spots or pores. 

 These are the orifices of the conceptacles, 

 which are globular cases immersed in the 

 substance of the receptacle, and communi- 

 cating with the outer surface by a pore (fig. 

 257). The central portion of the receptacle 



Fig. 257. 



Fucus canaliculatus. 



Section of a conceptacle of F. canaliculatus, containing 

 sporangcs, antlieridia, and paraphyses. 



Magnified 40 diameters. 



is filled up with a delicate network of jointed 

 filaments surrounded by a gelatinous sub- 

 stance, this medullary structure forming a 

 bond of union between the numerous concep- 

 tacles. The internal wall of the conceptacles 

 is lined with a dense mass of delicate jointed 

 filaments (fig. 257) standing vertically {para- 

 jjhyses), among which appear the stalked 

 spore-sacs alone in the dioecious and monoe- 

 cious forms, mixed with antheridia in the 

 hermaphrodite. The antheridia occur alone in 

 similar conceptacles in the monoecious and di- 

 oecious forms. F. canaliculatus is hermaphro- 

 dite (like Pycnophycus tuberculatus, which 

 however has antheridia only at the upper 

 part of the conceptacle, near the pore, spore- 

 sacs at the lower part) ; in F. serratus, cera- 

 noides, vesicidosus, and nodosus, the male 

 and female conceptacles occm-, usually on 

 distinct plants, but both kinds sometimes 

 occur on F. nodosus. The male and female 

 indi\dduals of the dioecious species may often 

 be distinguished, when mature, by the yel- 

 lowish colour the antheridia give to the re- 

 ceptacles ; and if these are exposed for a 

 short time to the air, the antheridia are ex- 

 pelled in masses through the pores of the 

 conceptacles, and form little orange-coloured 

 papillae. The female plants under similar 

 circumstances exhibit olive-coloured papillae 

 at the mouths of the pores, consisting of 

 masses of spores. 



The sporanges or spore-sacs consist of 

 ovate sacs, stalked on the walls of the con- 



ceptacle (fig. 257) ; they have a double mem- 

 brane, an outer, the sporange or perispore, 

 and an inner, the epispore; these are un- 

 distinguishable until the spores escape, but 

 then the epispore becomes evident as an 

 inner sac. The epispore encloses at first a 

 mass of ohve-colom'ed cell-contents ; in F. 

 canaliculatus {Pelvetia) this divides into two 

 spores, in F. nodosus {OzothalUa) into four, 

 and in F. serratus, vesiculosus, and the other 

 Fuci proper, into eight, by segmentation. 

 When mature, the sporange bursts at the 

 apex, the epispore enclosing the spores is 

 expelled, and makes its way towards the 

 pore of the conceptacle, and falls into the 

 water, where it undergoes the following 

 modifications. Taking F. vesiculosus as an 

 example, the expelled epispore encloses eight 

 spores, forming what Thuret calls an octo- 

 spore. This swells, and the spores become 

 rounded, separating from each other, and 

 the upper part of the epispore begins to dis- 

 solve. The spores become removed from 

 the lower part of the epispore (marked by 

 the impression of the stalk of the sporange), 

 and it then becomes evident that they are 

 enclosed in a third membrane, which is at- 

 tached to the epispore in the centre of its 

 base, so that as the spores emerge from the 

 dissolving summit of the epispore, the inter- 

 nal membrane becomes stretched upward, 

 until it finally bursts and sets the spores 

 free. These changes of the octospore are 

 generally passed through in about an hour, 

 sometimes much more rapidly. 



The antheridia consist of minute ovate 

 sacs, attached in great numbers to hair-like 

 filaments growing from the internal surface 

 of the conceptacle (fig. 258). When young. 



Fig. 258. 



Fig. 259. 



F, nodosus. 



F. serratus. 



Fig. 258. A branched cell bearing a perfect and imper- 

 fect antheridium. Magn. 200 diams. 



Fig. 259. Sac of an antheridiuiii nearly empty, with 

 a free spermatozoid. Magn. 400 diams. 



they are filled with colourless granular mat- 

 ter, but subsequently this becomes condensed 

 into little corpuscles {spermatozoids or an- 

 therozoids), forming a greyish mass dotted 

 with orange points. The sac is double, and 



