A series of memoirs on the utility of lichens written by Willemet[1310], Amoreux and Hoffmann, and jointly published at Lyons towards the end of the eighteenth century, represents the views as to the economic value of lichens held by scientific botanists of that time. All of them cite the various dye-species, and Hoffmann, as already stated, gives illustrations of colours that can be obtained. It has been once and again affirmed that Parmelia saxatilis yields a red colour, but Zopf[1311] denies this. It contains saxatillic acid which is colourless when extracted but on boiling gives a clear reddish-yellow to reddish-brown solution which dyes wool and silk directly without the aid of a mordant. Zopf[1311] observed the process of dyeing followed in South Tyrol: a layer of the lichen was placed in a cooking pot, above this a layer of the material to be dyed, then lichen and again the material until the pot was filled. It was covered with water and boiled three to four hours, resulting in a beautiful rust-brown and peculiarly fast dye.

Fig. 135. Parmelia omphalodes Ach. (S. H., Photo.).

Reddish- or rust-brown dye is also obtained from Haematomma ventosum and H. coccineum, a yellow-brown from Parmelia conspersa (salazinic acid), and other shades of brown from Parmelia perlata, P. physodes, Lobaria pulmonaria and Cetraria islandica.

Yellow lichens in general furnish yellow dyes, as for instance Xanthoria parietina which gives either brown or yellow according to treatment and Cetraria juniperina which forms a beautiful yellow colouring substance on 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[1312] 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 handsome 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 modification in the following external circumstances: