ROCCELLA TMfiTORIA.— DYEING ROCK-MOSS, OR ORCHEL. 
Class XXIY. CRYPTOGAMIA. Order IY. ALGffil. 
Natural Order, ALG^E, THE SEA-WEED TRIBE. 
The Lichens constitute an extensive natural group of plants, belonging to the class Cryptogamia, of the 
Linnsean system; and are commonly known in this country by the popular names of rock-mosses, tree mosses, 
and timestains. By the illustrious Linnaeus they were included in one great and complicated genus. Lichen, 
but Dr. Erick Acharius, a learned botanist of Stockholm, has since divided the whole series into three dis- 
tinct tribes, and forty-two genera : and subsequently, Borror, in this country, and Fries, in Germany, have 
greatly extended our knowledge of these interesting vegetables. In the plants of this Order, there are no 
regular roots, many of the species being attached by small fibres issuing from the under surface of the frond, 
or fixed to their place of growth as if by a sort of cement. They are equally destitute of stems, and also of 
leaves properly so called ; the part most analogous to a leaf, and which constitutes the body of the plant, 
being generally a crustaceous expansion, usually denominated th e frond, and by Acharius the thallus. The 
species are very numerous ; and not a few of them have at different times been employed in domestic econo- 
my, in medicine, and the arts. In Lapland, the branched coralline Lichen, Cenomyce rangiferina, is highly 
important in rural economy, as affording fodder for the rein-deer. A few species only have been used as 
food by men, but several sorts are eaten by goats, and other animals. Of these perhaps the most important 
in a dietetic point of view is the Cetraria Islandica, to be noticed hereafter ; and a species mentioned by Pro- 
fessor Pallas, as growing on the calcareous mountains of the great desert of Tartary, and described by 
Acharius under the name of Urceolaria esculenta. In Siberia, the lungwort lichen, Sticta pulmonacea is used 
in the making of ale, as a substitute for hops, and Parmelia physoda, Usnea plicata, and Ramalina farinacea, 
when eaten with salt, are used in some northern countries as food. Dr. Withering tells us, that the country 
people in some parts of England, make an infusion of Peltidea aphthosa, in milk, and give it to children 
affected with thrush, and that in large doses it excites purging and vomiting. Nor is this tribe of plants 
when administered internally, entirely harmless, for according to Pontoppidan, the yellow filamentous lichen, 
Evernia vulpina, is so poisonous, that it is employed for killing wolves, a carcase of some animal stuffed and 
smeared with the powder of it, mixed with pounded glass, being set as a bait. Several species are used for 
dyeing, and not a few were at one time considered as of great efficacy in the practice of medicine. Thus the 
common cup-moss lichen, Lichen pyxidatus, or Cenomyce pyxidata, Ach. was long regarded as an infallible 
nostrum for the hooping-cough ; the common ground-liverwort, L. caninus, or Peltidea canina, Ach., received 
its trivial name from the fame it had acquired as a specific in the cure of hydrophobia, and the tree lungwort 
or oak lungs, was equally renowned in former times for the cure of pulmonary complaints. At the present 
day, two species only, the Roccella tinctoria and Cetraria Islandica, the subjects of the following article, are 
retained in the list of the British Pharmacopoeias. 
The Orchel or Archil, Roccella tinctoria, is an indigenous Lichen, found sparingly on the maritime 
rocks of the south of England, particularly in Portland Island, and grows very abundantly on the sea rocks 
of the Cape Yerd, and also of the Canary Islands; and from both clusters it is exported in considerable 
quantities. In France it is called Orseille , and is used to a considerable extent in the southern provinces 
for dyeing silks, being collected on the rocky shores of the Mediterranean. By the Dutch, it is manu- 
factured into a paste called by them Lacmus or Litmus. This is sold in square masses about an inch in 
breadth, and thickness; hard and brittle, having the appearance of a violet coloured earth with white spots. 
The plant seldom exceeds two inches in height: it is firmly fixed to the rocks, and sends up a thick tuft of 
slender worm-like stems, round, pointed, often curved, more or less branched, smooth, of a white, grey, or 
brownish hue, studded about their upper part with numerous scarlet tubercles, or wartlike excrescences, 
replete with a white powder, which has been regarded by Redwig, or pollen or seeds, and by Geertner and 
others as a peculiar sort of gems or buds. The latter opinion has been established by Acharius, and lichens 
are now considered as gemmiparous plants, propagated only by bud-knots, or gongyli. 
Although many other species afford colours, this is the most valuable lichen as a dye-stuff. If we may- 
credit Tournefort, it was known to the ancients, being the Aeupyv of Dioscorides, and the Phycos thalassion of 
Pliny. It was collected in the islands of the Archipelago, and from one of these acquired the name of 
Purple of Amorgus. In modern times, according to Berthollet, it was prepared as an article of commerce at 
Florence, the fine violet colour which it was capable of producing, having been accidentally observed by a 
