IX THE STUDY OP LICHEN'S. 363 



the diverse and very evident reactions wliich it produces on the 

 thalli or the fruits of Lichens ; and here the colour produced by 

 the reaction, which in certain Lichens is of a purple red ("rouge 

 pourpre"), and in others yellow ("jaune"), is permanent*. 



We will first speak of the intense purple coloration ('^ pourpre") 

 which potash gives so soon as it is applied to the thalli or to 

 apothecia which contain clrysoplianic acid. The material thus 

 colourable occurs on the surface of those parts of Lichens (the 

 epithallus and the epithecium), and reveals itself by their natural 

 yellow or orange or red colour; tlie chrysophanic reaction, either 

 purple or very deep purple, shows itself at the very instant of the 

 application of the potash, whicli acts by dissolving the epithalline 

 or epithecial powder (/'. e. the molecular granulations wliich con- 

 tain the colourable material) into a liquid of a purple colour. It 

 is very easy to convince ourselves of the importance of this dis* 

 tinctive sign, according to its existence or non-existence in the 

 Lichens M-hich we are studying or determining. Thus^ for ex- 

 ample, a Lichen which is eminently chryso2)hanic is the common 

 Pki/scia jyarietinaf and its variety It/cluiea, which has been very 



often confounded with the Lecanora candclaria, Ach., and which 

 m a sterile state it is not always easy to distinguish ; but the 

 potash shows their differences instantly in the very least atom of 

 their thalli or their fruits ; for the candelm^ia is not changed in 

 colour by this reactive, whilst the lychnea becomes of an intense 

 purple. This is so evident that we are by these me^ins able to 

 recognize either the one or the other of these two Lichens, even 

 without opening the papers in wliich they may be enveloped, 

 provided the paper be permeable by the solution of potash ; for if 

 it be the lychnea^ the paper is innnediately coloured ; but if it be 

 the candehiria, the paper remains uncoloured. This absence of 

 reaction indicates that w^e must arrange the candclaria in the 

 group 0? Lecanora vitelUna, in which the potash does not produce 

 any cliange of colour. For the same reason we must refer to the 



* We shall speak further on of a modification of the yellow (*»jauiie") reac- 

 tion, which quickly changes into a red or reddish oelire (" rouge " or " rougeatre 

 oehrnee") in certain Lichens. 



t Neyerthcless T must mention that the forms of this species (and of the 

 neighbouring species) wliieh grow in tlie shade, and of which the thallus tlien 

 becomt^ green or grey, do not exhibit the chrysophanic reaction, except on the 

 circumfercnee of tlie thallus and on the epithecium. The same thing takes 

 place in JPhyscia Jtavicansy dirysojyhlhahna^ &c., in Lecanora muronan^ f. 



