SECT. iv. DYES ORCHIL. 303 



first, and remarkable for its long, pendulous, cylindrical 

 branches hanging down like bunches of bluish grey 

 hair. It is often attached to the branches of aged 

 larch trees, and is exceedingly picturesque. With the 

 exception of Evernia vulpina and flavicans, which are 

 brightly coloured, all the rest of the genus have dull 

 tints. The genus Eamalina has the dull tints of the 

 Evernia, and some species approach very nearly in form 

 to that genus. The Eamalina polymorphum and E. sco- 

 pulorum abound in dyes, while the E. calicaris is rich 

 in gluten. 



Lichens have lost much of their importance since 

 the discovery of the coal tar colours ; nevertheless they 

 afford dyes still in use. In many species the dying 

 principle is colourless like aniline ; but it yields the most 

 brilliant colours by means of alkalies. The Parmelia 

 parietina, common on walls and the roofs of houses, 

 gives the chrysophonic acid, a colourless liquid which 

 becomes bright yellow when treated with an alkali; 

 and in like manner the vulpinic acid, given by Evernia 

 vulpina, gives a brown dye. Notwithstanding the quiet 

 greyish green tints of the Eocella fuciforrnis and E. 

 tinctoria, no lichens are richer in the purple substance 

 known as orchil, from which, by means of soda or 

 potash, the valuable blue substance litmus is manu- 

 factured, so important as a test for acidity. Many 

 of the small moss-like lichens yield orchil, but none 

 in such abundance as the E. fuciformis, which grows 

 in Madeira, Angola, Madagascar, and South America. 

 Oxalic and usnic acids are produced by lichens; 

 indeed the usnic acid combined with green and yellow 

 resins seems to be more or less a constituent of 

 various lichens. It is evident that the colour of the 

 dyes is altogether independent of the colour of the lichen 

 from whence they are obtained. 



These aerial plants have a marvellous power of decom- 



