136 



POPULAR HISTORY OF LICHENS. 



in the market. Plants growing in arid situations in tropical 

 countries are found richest in colorific principles ; hence, as 

 compared with species from tropical Africa, Asia, or South 

 America, European species are worthless in commerce. Bur- 

 nett illustrates this, by stating £290 per ton as the value of 

 Canary Orchella-weed, while the same plant from Madeira 

 will only bring £140, and from Barbary from £80 to £45, 

 in the market. This is an instructive lesson on the influence 

 of climate in the production of changes in the chemical com- 

 position or products of Lichens. The estimated annual value 

 of the imports of Orchella-weeds and other dye-lichens many 

 years ago was stated at £60,000 to £80,000. Their value 

 has been gradually rising in the English market. Half a cen- 

 tury ago only inferior kinds were procured at prices ranging 

 from £20 to £200 per ton; now very fine qualities are im- 

 ported from various localities, probably at an average price 

 of £200 to £400 ; and they have been known to rise so 

 high as £1000 per ton. While Italy enjoyed a monopoly 

 in the manufacture of Orchill, large quantities were supplied 

 by Teneriffe, the Canaries, Azores, and neighbouring islands; 

 the inhabitants farmed out the right to gather the Orchella- 

 weeds, paying therefor considerable sums to the Government. 

 Prior to this the Orchella-weeds were known only in the 



