718 SYSTEMATIC BOTANY. 



vegetation of the polar regions and of mountain-tops. Eccamples 

 of the Genera: — Opegrapha, Verrucaria, Lecidea, Cladonia, 

 Peltigera, Usnea. There are about 2,500 species. 



Properties and Uses. — Several lichens possess nutritive pro- 

 perties from containing amylaceous stibstances, such are also 

 emollient and demulcent ; others contain bitter principles, which 

 render them tonic and astringent ; and several are important 

 as dyeing agents. A few possess aromatic properties. Some 

 lichens, as species of Variolaria, contain a large amount of 

 oxalate of lime. None are known to be poisonous. 



Cetraria. — C. isktndica, Iceland moss. — This lichen contains two kinds of 

 Btarchy matters — one called lichen starch, and the other inuUn : it also con- 

 tains a bitter principle {cetrarin). It is officinal in the British Pharma- 

 copoeia, and is emplo3^ed as a nutritious food, and as a mild mucilaginous 

 tonic in catan-h, consumption, &c. When used for food only, it should be 

 previously deprived of its bitterness : this may be done either by heating 

 it twice in water to near the boiling point of Fahrenheit, or by digesting it 

 in a weak alkaUne solution formed by adding half an ounce of carbonate of 

 potash to about a gallon of cold water, and afterwards washing it with 

 water. C. nivalis possesses somewhat simUar properties. 



Cladonia or Cenomyce. — C. rangiferina is the Reindeer Moss. It ia so 

 termed from constituting the food, especially in the winter mouths, of the 

 Reindeer. Cladonia {Scyphophorus) pyxidata is commonly termed Cup-moss : 

 this and other species have been employed as remedies in hooping-cough. 



Gyrophora (Unibilicaria). — Several species, denominated tripe de roche, 

 possess nutritive properties, and are used as food in the arctic regions. 

 Franklin and his companions owed their preservation in 1821, in a great 

 measure, to the use of these lichens as food. The Gyrophoras also possess 

 slight tonic properties, owing to the presence of a bitter principle. G. pustitlata 

 is one of the lichens used in this country by the manufacturers of orchil 

 and cudbear. (See Roccella and Lecanora.) It may be also made to pro- 

 duce a brown colour. 



Lecanora.— L. tartarea was fonnerly the principal lichen used in the pre- 

 paration of the dye called Cudbear. Cudbear is, however, now obtained 

 not only from it, but also from a number of other Lichens, as the species of 

 Roccella, &c. (See Roccella and Gyrophora.) L. Perella yields a ?imilar dye. 

 Two species of Lecanora, namely, L. esculenta and affinis, form important 

 articles of food both to man and animals generally in Fersia, Armenia, Tar- 

 tary, &c. They appear in some seasons in such enormous quantities, that in 

 certain districts they cover the ground to the depth of several inches, and 

 the natives believe they fall from heaven. L. esculenta is also found in 

 Algeria, Asia Minor, &c., and Dr. O'Rorke has endeavoured to prove that 

 this substance was the true manna of the Hebrews,— that which fed them 

 with regularity for forty years in the wilderness. 



Parmelia.—P. parietina was formerly regarded as a valuable febrifuge, 

 astringent, and tonic. It contains a yellow crystalline colouring matter, 

 called cJirysophanic acid, which is identical with the yellow colouriiig 

 principle of rhubarb. P. perlata is employed by the manufacturers of 

 orchil and cudbear. (See Roccella.) It is also reputed to possess diuretic 

 properties. 



Peltigera.— Peltigera (Peltidea) canina and P. rufescens are known in the 

 herb shops of this country under the name of Ground Liverwort. This 

 was formerly officinal in the London Pharmacopoeia, and regarded as a 

 specific in hydrophobia. 



Roccella, Orchclla Weeds.— 7?. fuciformis, R. tinctoria, and R. hypomecha, 

 under the common name of Orchella Weed, are the species usually met with 

 in this country. They are imported from various parts of the world, as the 

 Canary and Cape de Verd Islands, the Azores, Angola, Madagascar, Mauri- 

 tius, Madeira, South America, Cape of Good Hope, &c. In commerce they 



