IX THE STUDY OF LTCllEXS. 359 



for examplej the B. ^fontagnei, immersed in water, which in con- 

 sequence becomes milky ; when settled it deposits a Avhitish 

 powder, which contains erythric acid. The anatomical structure 

 of the thallus of the Boccell(B teaches us how it happens that this 

 colourable matter permits itself to be expressed by such a mani- 

 pulation ; for the surface of their thallus is not covered by any 

 tegumentary or cuticular layer, the cortex being simply composed 

 of short filaments (in length 0*015-0'025 millim., and in thickness 

 about pool millim.) juxtaposed and erect, so that their approxi- 

 mate summits constitute the surface of the thallus. Of this I 

 have given a representation in my ^Synopsis methodica Lichenum,* 

 vol. i. t. 8. f. 3. These cortical filaments have the narrow inter- 

 sticCvS between them, and also their summits, powdered over Avith 

 a white powder, which may also be seen, but much more rarely, 

 m the medulla formed by the entangled prolongations of the short 

 straight filaments of the cortex. On adding ammonia, we see, 

 under the microscope, the molecular granulations of this powder 

 to be immediately dissolved, and the preparation under examina- 

 tion becomes clear by the disappearance of this powder. 



The particular structure of the exto'ual portion of the thallus 

 explains liow the lichen, saturated with water, on being rubbed, so 

 readily parts with the free powder which covers and adheres to 

 the filamentous anatomical elements above mentioned. The wliitish 

 powder thus obtained, liquefied by a solution of hypochlorite of 

 lime, instantaneously assumes a red colour, which I call erythrinic^ 

 and which is very vivid, but somewhat fugitive. The same colour 

 immediately appears if we apply this reactive to the surface of 

 the thallus in question. For this purpose it is not necessary to 

 faftve a filtered solutiou, but it is sufficient to place in a bottle 

 with a wide mouth and a glass stopper a certain quantity of fresh 

 Vpochlorite of lime and to pour water upon it; the water is 

 quickly impregnated, and the liquid will continue clear if the 

 t>ottle be not shaken. A glass rod {'^ agitate ur''' chemice) dipped 

 lu the liquid, and applied to the thallus of the HocceUa rich in 

 colourable matter, immediately exhibits the beautiful erythrinic 

 action. Thus are we enabled to say what is the quantity of this 

 colourable matter which the diffefent species of the genus contain, 

 it being iu fact a sort of immediate analysis. "\Ve thus establish 

 ^ a fact that this matter is formed and excreted on the outside 

 of the gonidial layer, and, on the other hand, that towards the 

 interior, in the medulla, there are only feeble traces of it. 



On submitting a transverse slice of Roccella Montagnd to the 



^INX. PfiOC. — BOTAIJY, VOL. IX. 2 B 



