AS A SPECIFIC CHAKACTETl IN LICHENS." " 53 



of apothecia so easily removed by potash as in those of the triie: 

 L . ferrnginea \ it is at once dissolved out ^vithout being rendered: 

 purple, is carried away on the stirrer, and -diffused over the 

 thallus. In the ery throcarpous Cladoniw the same thing appeared 

 to occur; the natural rich crimson colouring- matter was at 

 once dissolved out, staining the podetia. In some cases, how- 

 ever, the colour was at once changed into brown; and in the 

 natural state the red apothecia of Gladonia frequently become 

 brown* as the result of age and desiccation, e. g, in the cornu^. 

 copioides group. I doubt, moreover, the propriety of describing 

 the reaction of potash on the red apothecia of Cladonia as 

 chrysojyJianic^ and on the podetia or folioles of the same species 

 as usnic. 



On account of its clirysophanic reaction, Nylander separates 



■ w 



Physcia parietma from P. candelaria. "The potash shows their 

 differences instantly in the very least atom of either their thalli or 

 their fruits ; for the candelaria is not changed in colour by this 

 reactive, whilst the Igchnea becomes of an intense purple. This 

 is so evident that we are by these means able to recognize either 

 the one or the otlier of these two lichens even without opening 

 the papers in which they may be enveloped, provided the paper be 

 permeable by the solution of potash" (p. 363). But, in exceptional 

 cases, I have found the reaction in jyarietina obscure [^.y. in 

 Hepp's No. 595] ; and Nylander himself admits that certain 

 forms of that species do not exhibit the reaction, save on the 

 periphery of the thallus, and on the epithecium. This occurs, he 

 admits, also in Fhjscia Jlavicans, P. chrgsoj)htkalma, and Placo^. 

 dimn murorum. Exceptions of tliis kind are sometimes so nume- 

 rous and of such a character, as to render the general rule quite 

 worthless, and altogether to invalidate the utility of the test. In 

 the fruited state, parietina and candelaria are sufficiently separable 

 by their sporldia; while the attempted distinction of sterile 

 (which may be abortive or degenerate as well as young) condi- 

 tions of lichens by chemical reaction appears to me to be at the 

 least fraught with danger. In no case have I been able to satisfy 

 myself of its safety or propriety. Nylander classes candelaria 

 with viielUnaj because they have tlie common property of non- 

 reaction with potash. But I have found the chrysophanic reaction 

 sometimes exhibit itself in the Lecanora. There are various 



* Vide author's paper on "Arctic Cladonia:;'— Trans. Botanical Sociot^^ of 

 Edint). vol. ix. p. 176. 



