13. Parmelia parietina, Ach.—Common Yellow Wall Lichen.
Parmelia parietina, Ach.; Lobaria parietina, Hoffm.; Lichen parietinus, Linn.; Common Yellow Wall Lichen. Usually sold in the herb shops under the name of common yellow wall moss. χρνσο φυλλον, hodie in Zacyntho, Sibth. Thallus foliaceous, membranaceous, orbicular, bright yellow: the lobes marginal, radiating, rounded, crenate, and crisped, granulated in the centre, beneath paler and fibrillose. Apothecia deep-orange, concave with an entire border (Hooker). This lichen has been the subject of repeated chemical investigation. According to Herberger [Buchner's Repertorium, Bd. xlvii. S. 179, 1834.], it contains two beautiful colouring matters (parmelia-yellow and parmelia-red), several alimentary principles (gliadin, sugar, starch, and gum), and three medicinal substances (soft resin, bitter matter, and volatile oil); besides wax, stearine, chlorophylle, and woody fibre. Rochleder and Heldt [Ann. d. Chem. u. Pharm. Bd. xlviii. S. 12, 1843; and Chem. Gazette, vol. ii. p. 162, 1844.] give the name of chrysophanic acid (C10H8O3) to the golden yellow crystallizable colouring matter, which, more recently, Schlossberger and Doepping [Ann. d. Chem. u. Pharm. Bd. i S. 295, 1844; Pharm. Journal, vol. iv.] have found to be identical with the yellow colouring matter of rhubarb (rheine, rheumine, rhabarbaric acid). In 1815, this was lauded by Dr. Sander [Die Wandflechte, ein Arzneymittel, welches die peruv. Rinde nicht nur entbehrlich macht, sonder die auch an gleichart. Heilkräften übertrifft, 4to. Sondershausen, 1815.] as a valuable substitute for cinchona bark in intermittents. He also gave it with success in hemorrhages and fluxes. Haller had previously spoken favourably of it as a tonic in diarrhoea and dysentery; and Willemet had found it useful in contagious autumnal fluxes. Subsequent experience, however, has not confirmed the favourable reports made of its medicinal power. The dose of it in powder is from ℥j to ℨj. It may also be in the form of decoction, tincture, and extract. Dr. R. D. Thomson [Lond. Ed. and Dub. Phil. Mag. July, 1844.] has proposed it as a test for alkalies, which communicate to its yellow colouring matter (called by him parietin) a beautiful red tint.