LICHENS. 59 



development in the tropics. In Spitzbergen, at about 

 thirty degrees latitude, only thirty species were found, 

 whilst at Madagascar, under the tropic of Capricorn, 

 they numbered five thousand. Hence it may be 

 inferred that these cryptogams are the most widely 

 diffused of all terrestrial plants. 



Dye Lichens. 



The most important economic use to which species 

 of lichens have been applied in the past was that of 

 the production of certain purple dyes, much in vogue 

 before the introduction of aniline. Dr. Lauder Lindsay 

 contended that these dyes were known from a remote 

 antiquity, and that they were alluded to in Ezekiel 

 (xxvii. 7), " Blue and purple from the isles of Elishah 

 was that which covered thee." The general name 

 of these dyes was orchil, or orchella ; and orchella 

 weed was long an important item in our trade im- 

 ports — reaching in value to from iJ^6o,ooo to ;^8o,ooo 

 per year. The various species of Roccella were im- 

 ported, under the names of Angola, Lima, Cape, or 

 Canary orchella weeds, for the manufacture of orchil 

 or cudbear. The English name was orcJiil, the 

 Scotch cudbear^ and the Dutch litmus. The first 

 was manufactured in the form of a liquid or paste, 

 of a rich purple colour ; the second occurred in the 

 form of a powder, of a crimson tint ; whilst the third 

 was only known in the form of small oblong cakes 

 of an indigo-blue colour. The colour was naturally 

 reddish, the blue tint being communicated by the 

 addition of alkalies. The principle of the manufac- 

 ture consisted in reducing the cleansed and powdered 



