226 PHYSIOLOGY 



Group 2. Neutral colourless substances insoluble in alkalies, but soluble 

 in alcohol, the solution not coloured by iron chloride. Exs. zeorin (C^H^O^, 

 a product of widely diverse lichens, such as Lecanora (Zeora) sulphurea, 

 Haematomma coccineum, Physcia caesia, Cladonia deformis, etc. and barbatin 

 (C 9 H 14 O), a product of Usnea barbata. 



Group 3. Brightly coloured acids, yellow, orange or red, all derivatives 

 of pulvinic acid (C ]8 Hi 2 O 8 ), a laboratory compound which has not been found 

 in nature. The group includes among others vulpinic acid (Ci 9 Hi 4 O B ) from 

 the brilliant yellow Evernia (Let/uiria) vulpina, stictaurin (CysH&Og) deposited 

 in orange-red crystals on the hyphae of Sticta aurata, and rhizocarpic acid 

 (CggHaoOe) chiefly obtained from Rhizocarpon geographicum : it crystallizes 

 out in slender citron-yellow prisms. 



Group 4. Only one acid, usninic (C, 8 H ]6 O 7 ), a derivative of acetylacetic 

 acid, is placed in this group. It is of very wide-spread occurrence, having 

 been found in at least 70 species belonging to very different genera and 

 families of crustaceous shrubby and leafy lichens. Zopf himself isolated it 

 from 48 species. 



Group 5. The thiophaninic acid (C 12 H 6 O 9 ) group representing only a 

 small number. They are all sulphur-yellow in colour and soluble in alcohol, 

 the solution becoming blackish-green or dirty blue on the addition of iron 

 chloride, with one exception, that of subauriferin obtained from the yellow- 

 coloured medulla of Parmelia subaurifera which stains faintly wine-red in 

 an iron solution. Thiophaninic acid, which gives its name to this group, 

 occurs in Pertusaria lutescens and P. Wulfenii, both of which are yellowish 

 crustaceous lichens growing mostly on the trunks of trees. 



II. LICHEN-ACIDS OF THE BENZOLE SERIES 



The larger number of lichen-acids belong to this series, of which 94 at 

 least are already known. They are divided into two subseries: I. Orcine 

 derivatives, and II. Anthracene derivatives. 



SUBSERIES I. ORCINE DERIVATIVES 



Zopf specially insists that the grouping of this series must be regarded 

 as only a provisional arrangement of the many lichen-acids that are included 

 therein. All of them are split up into orcine and carbonic acid by ammonia 

 and other alkalies. On exposure to air, the ammoniacal or alkaline solution 

 changes gradually into orceine, the colouring principle and chief constituent 

 of commercial orchil. Orcine is not found free in nature. The orcine sub- 

 series includes five groups : 



Group i. The substances in this group form, with hypochlorite of lime 

 ("CaCl"), red-coloured compounds which yield, on splitting, orsellinic acid. 

 Zopf enumerates seven acids as belonging to this group, among which is 



