664 



THE SUBDIVISIONS OF THE VEGETABLE KINGDOM. 



The Wrack-genus Fucus forms an exceedingly conspicuous feature of our sea- 

 shore flora. The shoot is flattened and ribbon-like, branching in one plane and 

 attached to stones, &c., by a sucker-like disc. In many species there is a midrib, as 

 also air-bladders. The tips of many of the branches are studded with little rugosi- 

 ties — really indicating 

 the presence of pear- 

 shaped hollows, the con- 

 ceptacles. From the lia- 

 ing of these conceptacles 

 project the oogonia and 

 branched filaments bear- 

 ing antheridia respective- 

 ly. As a rule the male and 

 female organs occur on 

 distinct plants, though in 

 some species the anther- 

 idia and oogonia occur 

 side by side in the same 

 conceptacle. The struc- 

 ture of the sexual cells 

 and the act of fertiliza- 

 tion (which occurs out- 

 side the mouth of the 

 conceptacle) have been 

 fully described on pp. 51, 

 52; they are represented 

 in figs. 376 and 377. 

 Sixteen species of Fucus 

 are distinguished, and 

 they occur for the most 

 part in the seas of the 

 northern hemisphere. 

 Fucus vesiculosv^ and 

 F. serratus are the com- 

 monest. Several other 

 genera are represented 

 in Britain, Pelvetia, Ascophyllum, Cystoseira, Halidrys, and Himanthalia. The 

 last-named genus is altogether peculiar, and consists of a top-shaped body at- 

 tached by its pointed end, whilst from the upper surface of the "top" arise 

 several ribbon -like outgrowths which branch repeatedly and attain to a length 

 of several metres. It is upon these ribbons that the conceptacles are borne. Of 

 exotic forms a few may be mentioned. Burvillcea from the southern seas resembles 

 a thick, fleshy Laininaria in habit; from the summit of its thick stipe arise a 



Fig. 377 Fuous vesiculosus. 



J Vertical section througl) a male conceptacle. 2 a portion of one of the shrubby, 

 branched hairs bearing antheridia. 8 Sperraatozoids escaping from the anther- 

 idia. * Spherical egg-cell with spermatozoids attached. ix50; 2x160; 

 ',*X 360. (After Thnret.) 



