22 HANDBOOK OF SEA- WE EDS. 



are branched sea weeds, covered also with tufts of closely set 

 hairs. Carpomitra Cabrerae, a rare species, bears, in common 

 with the two preceding species, its spores in a special receptacle. 

 In the first the receptacle is pod -like ; in the second knotted ; 

 and in the last mitriform. 



The concluding group of Algae is the Fucaceoe, including the 

 universally known sea wrack (Fucus). The frond in all of them 

 is jointless. They are reproduced by means of antheridia and 

 oogonia developed in conceptacles, clustered together at the 

 apex of the branches. Both from their bulk and their decided 

 sexual distinctions, they deserve to rank at the head of the 

 order. Of all sea-weeds they are also perhaps of the 

 greatest use to man. One of the most interesting among 

 them is the Gulfweed (Sargassum bacciferum), occupying a 

 tract of the Atlantic extending over many degrees of latitude. 

 Pieces of it, and of its congener, S. vulgare, are occasionally 

 drifted to our shores, and they consequently find a place in works 

 on British Algae, although they have no claim to be considered 

 native plants. On rocky coasts the various species of Fucus 

 occupy the greater part of the space between tide-marks, the 

 most plentiful being Fucus vesiculosus. F. serratus (Fig. 12) 

 is the handsomest of the genus, the other species being F. 

 nodosus, said to be the most useful for making kelp, and 

 F. canaliculatus. Halidrys siliquosa is remarkable for its spore 

 receptacles, which have quite the appearance of the seed vessel 

 of a flowering plant. The species of Cystoseira, chiefly con- 

 fined to the southern coasts, are also very interesting. Their 

 submerged fronds are beautifully iridescent, and the stems, of the 

 largest species at least, are generally covered with a great variety 

 of parasites, animal and vegetable, the former consisting of 

 Hydrozoa and Polyzoa, and other curious forms. Himanthalia 

 lorea is another remarkable plant. It has conspicuous forked 

 fruit-bearing receptacles ; but the real plants are the small 

 cones at the base of these, and from which they are shed when 

 ripe. 



As to conditions of site and geographical distribution, Algcedo 

 not differ from land plants. Latitude, depth of water, and 

 currents influence them in the same way as latitude, elevation, 

 and station operate on the latter ; and the analogy is maintained 

 in the almost cosmopolitan range of some, and the restricted 

 habitat of others. Not many extra-European species of Desmids 

 are known, but those of Diatoms are far more widely diffused, and 

 extend beyond the limits of all other vegetation, existing wherever 

 there is water sufficient to allow of their production ; and they 



