392 THE INHABITANTS OF THE SEA. 



their wide geographical distribution. Thus the Ulva latissima 

 and the Fnteromorpha compressa of our shofes thrive also in 

 the cold waters of the Arctic Sea, fringe the shores of the tropical 

 ocean, and project into the southern hemisphere as far as the 

 desolate head-lands of Tierra del Fuego. But few animals or 

 plants possess so pliable a nature, and such adaptability to the 

 most various climates. 



The Olive-coloured group of sea-weeds, or Melanospermese, 

 plays a much more considerable part in the economy of the 

 ocean. The common fuci, which on the ebbing of the tide im- 

 part to the shore cliffs their peculiar dingy colour, belong to this 

 class ; as well as the mighty Laminariae, which about the level 

 of ordinary low water, and one or two fathoms below that 

 limit, fringe the rocky shore with a broad belt of luxuriant 

 vegetation. 



The first olive-coloured sea-weed we meet with on the reced- 

 ing of the flood is the small and slender Fucus canaliculatus, 

 easily known by its narrow grooved stems and branches, and 

 the absence of air-vessels. Then follows Fucus nodosus, a large 

 species, with tough thong-like stems, expanding at intervals 

 into knob-like air-vessels, and covered in winter and spring with 

 bright yellow berries. Along with it we find the gregarious 

 Fucus vesiculosus, with its forked leaf traversed by a midrib, 

 and covered with numerous air-vessels situated in pairs at each 

 side of the rib. Finally, about the level of half-tide, a fourth 

 species of fucus appears, Fucus serratus, distinguished from 

 all the rest by its toothed margin and the absence of air- • 

 vessels. 



These four species generally occupy the littoral zone of our 

 sea-girt isle, being found in greatest abundance on flat rocky 

 shores, particularly on the western coasts of Scotland and Ireland, 

 where they used formerly to be burnt in large quantities for 

 the manufacture of kelp or carbonate of soda, which is now 

 obtained by a less expensive process. In Orcaflia alone more 

 than 20,000 persons were employed during the whole summer 

 in the collection and incineration of sea-weeds, a valuable re- 

 source for the.poverty-stricken islanders, of which they have- 

 been deprived by the progress of chemical science. 



The fuci are, however, still largely used, either burnt or in a. 

 fermented state, as a valuable manure for green crops. Thus- 



