88 A Short Talk on Lichens. [Sess. 



treated with alkalis as soda and potash. These pigments 

 depend upon the presence of special acids in the thalli of 

 the lichens. Some of the crustaceous lichens are employed 

 in France in the manufacture of oxalic acid. Gum has been 

 got from Eamalina fraxinea, and the bases of perfumes from 

 Usnea, Eamalina, and Cladonia. 



As medicines some lichens were formerly highly esteemed, 

 but their virtues were often more imaginary than real. They 

 were used as demulcents, febrifuges, astringents, purgatives, 

 and tonics. Iceland moss {Cctraria islandica) is the only 

 species which has retained a place in British pharmacy, but 

 it is now principally employed as an article of diet for in- 

 valids and convalescents, and is being gradually superseded 

 even in this by other more nutritious productions. This 

 same lichen is extensively used in Iceland as food. It 

 contains about 47 per cent of lichenine, a form of starch. 

 " Tripe de roche " and the Gyrophoras are eaten in the ex- 

 tremities of hunger, as was done by Dr John Franklin and 

 his men. Lecanora esculenta, manna-bread, is eaten by the 

 Tartars and other tribes. Several lichens are ground to 

 powder and mixed with meal or flour. Their value as food 

 consists in the starch in their composition. Some lichens are 

 extensively used as food for cattle, especially Cladina rangi- 

 ferina, to which I shall more particularly refer farther on. 

 Usnea yields food for goats and reindeer. Alectoria jubata 

 is sot from felled trees when the snow is too frozen for the 

 reindeer to get their common food. 



How varied, too, are the effects produced by the presence 

 of lichens on scenery ! Rugged rocks, wayside dykes, forest 

 trees, barren heaths, arctic tundras, the ruined castle, and 

 the Highland cottage, are all beautified by their covering of 

 lichens. Their form, their power of deriving sustenance 

 almost entirely from the atmosphere, their wonderful en- 

 durance and vitality, their ability to repair broken-off pieces, 

 all show their peculiar fitness for the work they are designed 

 to accomplish in the economy of nature. 



Lichens are cellular perennial cryptogamic plants having 

 affinities both with fungi and algae. Their position among the 

 cryptogamia is between these two, and as Nature has no sharp 

 and fast lines in her divisions, her boundaries generally over- 



