AS A SPECIFIC CHARACTEB IN LICHENS. 01 



to find any trace of red colouring-matter iu the genus Moccella 

 or in Lecanora parella * ! 



VI. Colour-results vary not only with the scale on which expe- 

 riment is conducted, but with the most minute and apparently 

 trivial of its details. Thus botanical testing, according to the 

 pseudo-system of Ny lander and Leighton, gives results frequently 

 quite of an opposite kind to those of experiment on dyeing-proper- 

 ties, and these, again, as conducted in the laboratory, on the small 

 scale, to the results obtained by the archil-manufacturer, on the 

 large scale. In the following dye-lichens which yield Archil to the 

 manufacturer, no corresponding reaction occurs wdth bleaching- 

 solution applied on Nylander's plan : — Umhilicaria (no reac- 

 tion save exceptionally) ; Boccella (reaction, where it occurs, 

 does not coiTespond to colorific value) ; Parmelia perJata^ Lecanora 

 parella, glaucoma^ and calcarea. On the other hand, a blood-red or 

 crimson is developed by the testing-process in certain non-dyeing 

 species, e, g. Parmelia sinuosa, Borreriy rugosa, and acetahulnm. 



At the Paris Exhibition (1867) I was struck with the great 

 variety of quality {e,g, shades of colour) in products essentially 

 the same, attributable, apparently, to slight modifications of the 

 process of manufacture. Darwin remarks, " The chemical quali- 

 ties, odours, and tissues of plants are often modified by a change 

 which seems to us slight.'^ He gives several instances (hemlock, 

 aconite, digitalis, rhubarb, &c.), which are " remarkable because 

 it might have been thought that definite chemical compounds 

 .would have been little liable to change, either in quality or 

 quantity " f- An apt illustration is to be found in the very dif- 

 ferent products obtainable by chemists, on the one hand, and 

 archil-manufacturers, on the other, from a single lichen, Hoc- 

 cella tincforia, apparently according to mere difierences in its 

 place of growth. Archil-manufacturers, as I have elsewhere 

 shown, constantly recognize the fact that very different tinctorial 

 values are to be attributed to the same hotanical species of ''Orchella- 

 weed'* from different localities J. 



* Creirs * Chemische Annalen,' 1799, vol. ii. p. 81, in note; quoted in Krem- 

 pelhuber's ' Geschichte der Lichenologie/ vol. i. p. 95 (1867)- 



t On Variation of Animals and Plants under Domestication, vol. ii. p. 274 



(1868). 



{ Journ. of Botany, 1868, vol. vi. p. 107. The irregularities of colorific re- 

 sults with reagents of the same class, and the causes of modification of colour- 

 results in the same species, are subjects illustrated more fullj in the * Pliytd- 

 logist,' 1854, vol. V. pp. 181-2. 



