USES OF LICHENS. 



89 



being a most deceptive guide. The genera containing the 

 most valuable dye species are Roccetta, Lecanora, Umbilica- 

 ria, Parmeiia, Urceolaria, Physcia, and Ramalina. A few 

 species belonging to one or more of these genera have long 

 been employed by manufacturers in the preparation of or- 

 chill, cudbear, or litmus, such as Uoccella tinctoria weAfu- 

 ciformis by the English orchill maker, or Lecanora tarta- 

 rea by the Scotch cudbear-maker and Dutch litmus-maker. 

 Other species have recently been introduced, either as sup- 

 plementary or substitutional species, such as Umhilicaria 

 pustulata, Parmelia perlata, and Lecanora pattescens var. 

 j)arella. For the purposes of British manufacture none of 

 these are collected from the rocks of our own highlands and 

 islands, but are procured from the African coasts and islands 

 or the mountains of Norway, at a considerable expense ; 

 while there is reason to believe that many species possess- 

 ing similar, if not equally valuable, colour-yielding proper- 

 ties, might be gathered at home at an infinitely cheaper rate. 

 When the cudbear manufacture, which is now extinct in 

 Scotland, flourished in Leith and Glasgow, large quantities 

 of Lecanora tartarea were collected by the peasantry of the 

 western highlands and islands ; and the revival and extension 

 of this traffic would probably prove a great boon to that 



