CETRARIA. 155 



level ; but, in general, its presence is indicative of a very cold 

 climate. In the Arctic Circle it is found at the sea-leyel, 

 and it grows on the bleak steppes of Central Russia, Asia, 

 and North America ; but as it spreads southwards it climbs 

 the mountains. Its brown colour and the beautiful blood- 

 red stains frequently found at its base are ingeniously ascribed 

 by Schnedermann to various salts formed, with ammonia ab- 

 sorbed from the air, or with iron taken up from the soil, by 

 Cetraric acid, — the peculiar bitter principle which resides in 

 the cortical layer of the plant. With ammonia this acid 

 forms a yellow salt, whose solution in w 7 ater becomes brown 

 on exposure to the air ; and the cetrarate of ammonia, thus 

 formed, causes a red reaction with persalts of iron. The 

 composition and products of Iceland-moss have been studied 

 by several chemists, who have detected in it starch to the 

 extent, according to Berzelius, of 80 per cent., including 

 both Lichenin and Inuline; gummy and waxy matters, the 

 former also to a considerable extent ; a bitter principle, 

 cetraric acid ; a fatty principle, lichestearic acid (Xe^^, 

 lichen, and areap, fat) ; fumaric acid, which exists also in 

 the common garden fumitory (Fumaria officinalis); gallic 

 acid, the astringent principle of galls ; uncrystallizable 

 sugar i and various salts, such as the bitartrate of potash, 



