FUCUS. 



[ 340 ] 



FUCUS. 



is filled up Tvatli a delicate network of jointed 

 filaments surrounded by a gelatinous sul> 

 etance, this medullary structure forming a 

 bond of imion between the numerous cou- 

 ceptacles. The internal wall of the con- 

 ceptacles is lined with a dense mass of de- 

 licate jointed filaments (fig. 253) standing 

 vertically (jMraphyses), among which ap- 

 pear the stalked sjwre-sacs, alone in the 

 dioecious and monoecious forms, mixed with 



Fig. 253. 



Section of a concfiitaLlu ui' i . i.uialiculatus, containing 

 sporanges, antheridia, and paraphyses. 



Magnilied 40 diameters. 



antheridia in the hermaphrodite. The an- 

 theridia occur alone in similar conceptacles 

 in the monoecious and dioecious forms. F. 

 canaUculatiis is hermaphrodite (like Pycno- 

 phyctts tuhercidatus, which, however, has 

 antheridia only at the upper part of the 

 conceptacle, near the pore, spore-sacs at the 

 lower part) ; in F. serratus, ceranoides, vesi- 

 ctdosus, and twdosxs the male and female 

 conceptacles occur usually on distinct plants; 

 but both kinds sometimes occur on F. nodo- 

 sus. The male and female individuals of 

 the dioecious species may often be distin- 

 guished, when mature, by the yellowish 

 colour the antheridia give to the recep- 

 tacles; and if these are exposed for a short 

 time to the air, the antheridia are expelled 

 in masses through the pores of the con- 

 ceptacles, 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 sj7oranges or spore-stacs consist of 

 ovate sacs, stalked, on the walls of the con- 

 ceptacle (fig. 253) ; they have a double 

 membrane — an outer, the sporatu/e or j)eri- 

 spore, and an inner, the epispore : these are 

 undistinguishable until the spores escape ; 

 but then the epispore becomes evident as an 

 inner sac. The epispore encloses at first a 

 mass of olive-coloured cell-contents ; in F. 

 canalicidattts {Pelvetia) this divides into two 



spores, in F. nodosus (Ozothallia) into four, 

 and in F. serratus, vesicidvsus, and the other 

 Fuel proper, into eight, by segmentation. 

 When matm^e, 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. vesiculostis as an 

 example, the expelled epispore encloses 

 eight spores, forming what Thuret calls an 

 octospore. This swells ; and the spores be- 

 come rounded, separating from each other ; 

 and the upper part of the epispore begins to 

 dissolve. 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 episjiure in the centre of its 

 base, so that as the spores emerge from the 

 dissolving summit of the epispore the in- 

 ternal 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-liko 

 filaments growing from the internal surface 

 of the conceptacle (fig. 254). When young, 



Fig. 254. 



Fig. 255. 



Fig. 2.54. A branched cell of F. nodosus, bearing a per- 

 fect and an imperfect antheridium. Magn. 200 dianis. 



Fig. 2.55. Sao of an antheridium of F. serratus, nearly 

 empty. Magn. 400 diams. 



they are filled with colourless granular 

 matter ; but subsequently this becomes con- 

 densed into little corpuscles (spermatozaids 

 or antherozoids), forming a greyish mass 

 dotted with orange points. The sac is 

 double ; and the internal one is expelled 

 from the outer like the epispore from the 

 sporange, and fuids its way out from the 

 pore of the conceptacle. The spermatozoids 

 which fill up the central part begin to move 

 actively ; and the sac soon bursts at one or 

 both ends to discharge them. The sperma- 

 tozoids (fig. 255) are excessively minute, 

 transparent bodies, scarcely 1-5000" long, 

 enclosing a granule of an orange-colour in 



