392 THE INHABITANTS OF THE SEA. 
their wide geographical distributiop. Thus the Ulva latissima 
and the Enteromorpha compressa of our shores thrive also in 
the cold waters of the Aretic 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 gzoup of sea-weeds, or Melanospermee, 
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 Laminariz, 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 Mucus canaliculatus, 
easily known by its narrow grooved stems and branches, and 
the absence of air-vessels. Then follows Mucus 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, Mucus 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. /n Orcadia 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 
