LICHENS AS DYE-PLANTS 417 



boiling. Teloschistes flavicans and Letharia vulpina yield very similar yellow 

 dyes, and from Lecanora parella (Fig. 39), Pertusaria melaleuca and Usnea 

 barbata yellow colours have been obtained. Candelariella vitellina and 

 Xanthoria lychnea both contain yellow colouring agents and have been 

 employed by the Swedes for dyeing the candles used in religious ceremonies. 

 g. Collecting of Dye-lichens. Lauder Lindsay^ made exhaustive 

 studies of dye-lichens both in the field and in the laboratory, and recorded 

 results he obtained from the micro-chemical examination of 540 different 

 specimens. He sought to revive and encourage the use of their beautiful 

 colour products among country people; he has given the following practical 

 hints to collectors : 



1. That crustaceous dwarf pale-coloured species growing on rocks, and 

 especially on sea-coasts, are most likely to yield red and purple dyes similar 

 to orchil, cudbear or litmus; while on the other hand the largest, most hand- 

 some foliaceous or fruticose species are least likely. 



2. That the colour of the thallus is no indication of colorific power (in 

 orchil lichens), inasmuch as the red or purple colouring substances are the 

 result of chemical action on crystalline colorific "principles" previously 

 devoid of colour. 



3. That alterations in physical characters, chemical composition and 

 consequently in dyeing properties are very liable to be produced by modi- 

 fication in the following external circumstances ; 



(i) Degree of moisture. 



(ii) Degree of heat. 



(iii) Degree of exposure to light and air. 



(iv) Climate. 



(v) Elevation above the sea. 



(vi) Habitat ; nature of basis of support. 



(vii) Age. 



(viii) Seasons and atmospheric vicissitudes, etc. 

 August has been recommended as the best month for collecting dye- 

 lichens : i.e. just after the season of greatest light and heat when the 

 accumulation of acids will be at its maximum. 



Some of the acids found useful in dyeing occur in the thalli of a large 

 number of lichens, many of which are too scantily developed to be of any 

 economic value. Thus salazinic acid which gives the effective yellow-brown 

 dye in Parmelia conspersa was found by Zopf in 13 species and varieties. 

 It has since been located by Lettau^ in 72 different lichens, many of them, 

 however, with poorly developed or scanty thalli, so that no technical use 

 can be made of them. 



^ Lindsay 1855. ^ Lettau 1914. 



S. L. 27 



