MCHEjrS, 



491 



ployed to tke greatest extent, because most uniformlT applicable, was Helot's 

 ammonia test. The follo%ving combination is that most favorable for the de- 

 velopment of the coloring matter of the lichens — viz., the presence 



1. Of icater as a solvent menstruum. 



2. Of atmospheric oxygen, 



3. Of ammonia^ in the state of vapor or in solution, and 



4. Of a moderate degree of heat ; 



And according as the proportion of these combining elements varies, so do 

 the kind and amount of color educed by them. This combination is the 

 foundation of all the processes for the manufacture of the lichen dyes through- 

 out the world, however different these may appear to be in detail or results. 



I believe it may come to be a matter of great commercial importance to dis- 

 cover, at home or abroad, some cheap and easily-procurable substitute for the 

 Moccellas, which are gradually becoming scarce, and consequently valuable in 

 European commerce, having sometimes fetched, in times of scarcity, no less 

 than £1,000 per ton. No plants can be so easily collected and preserved as 

 lichens — requiring merely to be cleaned, dried, pulverised, and packed; and 

 if their bulk be an objection to transport, their whole colorific matter may be 

 collected in the way I have already mentioned. Ascending to the verge of 

 eternal snows, and descending to the ocean level — with a geographical difi'usion 

 that is co-extensive with the surface of our earth, it is difficult to say where 

 lichens shall not be found. There are myriads of small rocky islets in the 

 boundless ocean, and there are thousands of miles of barren rocky coast and sterile 

 mountain range in every part of the world, which, though at present imfit to 

 bear any of the higher members of the vegetable kingdom, are yet carpeted and 

 adorned with a rich covering of lichens, and of those very species too, which 

 I have ah'eady spoken of as prolific in colorific materials. I sincerely believe, 

 therefore, that a more general attention to the very simple tests just enume- 

 rated, would ultimately result in a greatly extended use of the lichens as dye 

 agents. What renders it very probable that etforts in this direction are likely 

 to meet with success is the gi-eat similarity of species found all over the world. 

 It has been repeatedly noticed that the European species, which, of course, 

 are best known, diff'er little from those of North America, Dr. Eobert Brown 

 remarked the same fact with regard to New Holland species, and Humboldt 

 also recognised the similarity in natives of the South American Andes. Of a 

 large collection made by Professor Royle, in the Himalayas, Don pronounced 

 almost every one to be identical with European species. From txamining the 

 raw vegetable products, sent by different countries to the Great Exhibition of 

 1851, I am satisfied that, even now, there are many fields open for the esta- 

 blishment of an export trade in Eoccellas and other so-called orchella weeds." 

 I there saw specimens of good dye lichens from almost every part of the world, 

 including our own young colonies; and as a single instance of their probable 

 value, I may introduce here the copy of a note appended to a specimen of 

 orchella weed from the island of Socotra, contained in the Indian collection of 

 that exhibition, " abundant, but unTcnown as an article of use or commerce. 

 Also abundant on the hills around (Aden) and mighthe made an article of trade." 

 Eoccellas from this source are estimated as worth £190 to £380 per ton. I 

 believe that a similar statement might be made with regard to the countless 

 islands of the broad Atlantic and Pacific, which may, at some future period, 

 perhaps not far distant, be found to be rich depots of orchella weeds, just as 

 some of them are, at present, rich fields of guano, and may, as such, become 

 new nuclei of British commerce and enterprise. Even at home, in the imme- 

 diate vicinity of Edinburgh, or, to restrict our limits still more narrowly, 

 within the compass of Arthur's Seat, there are not a few very good dye-lichens, 

 which require merely to be scraped with an old knife or similar instrument, 

 from the rocks to which they adhere, and subjected to the ammonia process al- 

 ready mentioned. Of twelve specimens thus collected at random one morning, 

 I found no less than three yielded beautiful purple-red colors, apparently as 

 fine as orchil or cudbear, while the others furnished rich and dark tints of 

 brownish -red, brown and olive-green. 



Dr. Lindley's communication was illustrated with specimens of coloring 



