SEAWEEDS. 289 



attached, but is a mere sucker, sticking tightly to the surface, 

 and taking no part in the absorption of food for the plant, 

 which is effected by the entire general surface of the frond 

 from the surrounding waters, in which it floats in a more or 

 less erect attitude, but yielding to every movement of the 

 sea. 



The seaweeds are all reproduced by spores, but the structure 

 and production of these differ in the different groups, some 

 being asexual, and others the result of a distinct sexual pro- 

 cess. To this matter we shall give further attention by and 

 by. 



The most striking seaweeds owing 

 to their size and abundance are 

 those comprised in the Fucacca, all 

 the species of which are olive-brown 

 in colour. There are four species 

 of Fucus which are very abun- 

 dant on our shores, as well as 

 representatives of other genera 

 included in the family. On the 



highest of the rocks, that only be- CHANNELLED WRACK . 



come covered by high spring tides, 



and are only washed by rough seas, there grows in abundance 

 a little leathery plant called the Channelled Wrack (Fucus 

 canaliculatus] . During the greater part of its existence it 

 is dry and shrivelled and of black hue, but when covered 

 by the tide it absorbs the water, and becomes soft, with an 

 olive-brown tint. The frond is much branched, the segments 

 long and narrow, the edges being turned in so that on one side 

 they appear to be deeply channelled. It is the smallest of our 

 species of Fucus, arid is readily distinguished from its con- 

 geners, not only by its size, but by the channel-like folding, 

 the absence of air bladders, and the lack of a mid-rib. At the 

 extremity of some of its fronds there are irregular warty pod- 

 like organs of a dark orange tint. These are known as the 



