LICHENS. BLADDER FUCUS. 27* 
substance generally adopted for colouring the spirits of 
thermometers. And it is a remarkable circumstance 
that, as exposure to the air destroys its colour upon 
cloth, so the exclusion of the air produces, in a few 
years, a like effect upon the fluid in those tubes ; but 
on breaking the tubes the colour is restored. 
287. ICELAND LICHEN (Lichen islandicus) is a leafy, 
membranous, vegetable production, of brownish green colour, 
jagged at the edges, and fringed, having large and purplish 
brown saucers or shields. 
The name of this lichen is derived from that of the 
island in which it chiefly grows. It is, however, also 
found in the Highlands of Scotland, and in some of the 
northern parts both of England and Wales. 
It abounds with nutritious mucilage; and, after hav- 
ing been steeped in water to extract its bitter and 
laxative qualities, it is sometimes used as medicine in 
coughs and consumptions. One ounce of Iceland 
lichen, boiled in a pint of water, yields about seven 
ounces of mucilage. The inhabitants of Iceland pre- 
pare from it a kind of gruel, which they mix with milk. 
They also boil it in several waters, and then dry and 
make it into bread. In Germany a durable brown dye 
is made by means of it; and, under another mode of 
preparation, it imparts an excellent black tinge to white 
"woollen yarn. 
288. BLADDER FUCUS (Fucus vesiculosus) is a species 
of sea-weed, of flat shape, with a middle rib, the edges entire, 
forked, and sometimes tumid at the ends, and furnished with 
several air bladders imbedded in the substance of the plant. 
By far the most important application of this, one of 
the commonest of all our marine plants, is for the 
making of kelp, which, in Scotland, affords employment 
to many industrious families. So lucrative and so 
highly esteemed is the bladder fucus, and some other 
plants nearly allied to it, that the natives of several 
parts of the Western Islands have rolled large masses 
