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 lin- 

 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. 876 and 377. 

 Sixteen species of Fucus 

 are distinguished, and 

 they occur for the most 

 part in the seas of the 

 northern hemisphere. 

 Fucus vesiculosus 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 outgrov/ths 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. Durvilloea from the southern seas resembles 

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



Fig, 317.— Fucus vesiculosus. 



1 Vertical section through a male conceptacle. 2 a portion of one of the shrubby, 

 branched hairs bearing antheridia. s Spermatozoids escaping from the anther- 

 idia. ■* Spherical egg-cell with spermatozoids attached. 1 x 50 ; 2 x 160 ; 

 3, 4 X 350. (After Thuret.) 



