118 FOOTNOTES FROM 



often growing together with it on the same rock, is very 

 extensively employed in the south of France. This is 

 the famous Perelle d'Auvergne (Lecanora parella), which 

 imparts those beautiful and brilliant hues to French 

 ribbons, which are so much admired. The common 

 yellow wall-lichen (Parmelia parietina), so abundant 

 everywhere, yields a beautiful golden yellow crystalliz- 

 able colouring matter called crysophanic acid, which is 

 identical with the yellow colouring matter of rhubarb ; 

 and like orchil litmus, it may be used as a test for 

 alkalies, as they invariably change its yellow colour 

 into a vivid red tint. A beautiful and valuable crimson 

 pigment, occasionally employed by artists, is the product 

 of a dark-brown shrubby lichen (Cornicularia aculeata), 

 very common on the hills ; while the common stone 

 lichen (Parmelia saxatilis), which forms grey rosettes on 

 almost every wall, rock, and tree, is still collected abund- 

 antly by the Scottish peasantry, under the name of stane- 

 raw, to dye woollen stuff of 'a dirty purple or reddish- 

 brown colour. On the low rocks, on the summits of all 

 the loftiest Highland hills, there is a curious leafy lichen 

 (Parmelia fahlunensis), found abundantly, scorched ap- 

 parently by the sun into a black cinder. Of all lichens, 

 this species, judging from its outward colour and appear- 

 ance, would seem to be the least capable of yielding 

 colouring matter ; and yet when treated in the ordinary 

 way, it yields a brilliant pink, cherry, or claret colour, 

 which in France has been applied to so many useful pur- 

 poses, that the lichen in consequence has obtained the 

 common name of " Herpette des Tenturiers." But it is 

 needless to enumerate all the different species of lichens, 



