ROCCELLA TINCTORIA. ORD. LIV. Algz. 109 
Gen. Char. Frond between coriaceous and cartilaginous, rounded or plane, 
branched. Fructifications orbicular, adnate with the frond: seed-bearing 
portion a plano-convex disc, circumscribed by a margin of the same sub- 
stance as the frond, and covering a’black, compact, lentil-shaped, mass, 
immersed in the frond. . : 
Spec. Char. Frond rounded, glaucous-green, branched, and nearly erect. 
Fructifications scattered, elevated, with the disc plane, glaucous, and 
pruinose, even with the margin which is formed by the frond. 
THIS species of Lichen is the \ynv of Dioscorides, and the Phycos Tha- 
lassion of Pliny. It is an indigenous plant to our own country, growing on 
the maritime rocks of the south of England, particularly in Portland Island ; 
but it is not found in any great abundance. It grows very plentifully in 
the Levant, Canary Islands, &c. from whence it is chiefly collected to supply 
the markets. The Canary Islands alone are said to produce two thousand 
six hundred quintals annually, and it is from this abundance of Orchall 
that the ancients gave them the name of the Purple Isles.* Mr. Macintosh 
of Glasgow, who is, perhaps, the largest consumer of this plant in Europe, 
reckons the kind brought from the Canaries as by far the most valuable ; 
for while much of that imported from other countries is not worth 
£30. per ton, the best canary-weed (as it is called) fetches upwards of £200. 
per ton. From this Lichen is prepared the Argol or archil, so much used 
as a dye-stuff. ‘The Roccella tinctoria is a small species of lichen, from two ~ 
to four and even six inches in height, firmly fixed to the rocks by a solid 
base, from which rises a tuft of small, round, smooth, acutely pointed stems, 
more or less branched, of a whitish gray or brownish hue, and studded 
‘towards their upper part with scattered tubercles,+ replete with a white 
powder, which some consider to be the true fructification, but the real 
fruit, as described by Acharius, is of a much darker colour and rarer 
occurrence. 
* Mém. de I’Acad. des Inscriptions, iv. p. 457. 
4+ Gertner considers them as a peculiar sort of germs or buds, which opinion has 
been established by Acharius.  Lichens are now ranked as gemmiparous plants, propa- 
gated only by bud-knots, or gongyli. 
