Dyeing Properties of Lichens. 231 
XV. Simple maceration in a weak solution of ammonia, 
aided by a moderate heat and moisture, is the surest and 
simplest means of evolving the red colouring matters of the 
lichens. 
XVI. Alcohol is an excellent solvent of the colorific prin- 
ciples of the plants, presenting them in a form readily acted 
on by chemical substances. Its use on the small scale is ex- 
ceedingly convenient. The reaction of ammonia on a boiled 
alcoholic solution, allowed to stand for three days, is gene- 
rally the same in tint, though notin degree, as on an aqueous 
solution exposed to the air for very long periods (1 to 12 
months); but in some cases they differ essentially.— Vide 
Table xiv. 
This difference is probably, in part, attributable to the 
small quantity of materials operated on, and the short period 
of maceration in the former case, and to the larger quantity 
of materials and the abundant exposure to- atmospheric oxy- 
gen in the latter. 
XVII. The non-evolution of colour in many cases may 
arise from— 
a. Alcohol or water not being the best or proper solvent 
menstruum of the colorific principles in any particular 
instance. 2 
6. Ammoniacal maceration not being the proper means 
of converting the colorific into coloured substances. 
c. The plant not containing colorific principles having 
‘the same chemical composition as orcine, &., or 
showing similar reactions with chloride of lime and 
ammonia. 
XVIII. If we accept, meanwhile, Stenhouse’s and Helot’s 
tests as sufficiently accurate indicators of colorific value, we 
should arrange the lichen genera, which contain species 
yielding colouring matters—according to their value—as 
follows :-— 
1. Roccella, 5. Urceolaria, 9, Ramalina, 
2. Lecanora, 6. Parmelia, 10. Lecidea, 
38. Umbilicaria, 7. Evernia, 11. Isidium, 
4, Gyrophora, 8. Borrera, 12. Sphzrophoron, 
species of which yield fine red colouring matters; and 
