AS A SPECIFIC CHARACTER IN LICHENS. 55 



delicate; in Lecanora suhjusca it occurs distinctly only in those 

 forms which have a distinct white crustaceous thallus, e. g. tntu- 

 mescens. Sometimes a corticolous thallus is so thin and effuse, 

 though white, that the lemon-yellow or olive-green reaction might 

 be attributed to the subjacent bark, e. g. in some forms of Pertu- 

 saria communis and Lecanora suhfusca ; but that the reaction, 

 even in such cases, is attributable to the lichen, I hold proven by 

 the fact that I have tested the adjacent still thinner thallus of 

 Opegraphay or other genera or species, without the development of 

 the same reaction. 



C. Green-red reaction — where the greenish or yellowish tint 

 first developed by potash passes more or less rapidly or gradually 

 into a reddish or brownish-r<?^ colour. — It appears to me that this 

 distinction of Nylander's, the permanency or transiency of the 

 green or yellow, is a most artificial and unnecessary one; for I 

 find it does not hold good in the very species and genera selected 

 by himself as typical. Thus Lecanora cinerea, on the one hand, 

 and the Cladoniw, on the other, yielded me a series of results dif- 

 ferent from those recorded by himself or Leigliton. A large suite 

 of specimens of X. cinerea in my own herbarium yielded me, for the 

 most part, negative results, both with potash and bleaching-solu- 

 tion. In a few exceptional cases (3 Irish specimens, 1858, and 

 2 Norwegian, 1857) various tints, from olive-green to bright 

 lemon-yellow were developed by potash ; but in no case did the 

 colour in question change to red. Parmelia acetabulum^ says 

 Ny lander, gives the same reaction as L. cinerea ; while, in my hands, 

 it neither yielded the same reaction with bleaching-solution nor 

 with potash, resembling P. Borreri as to the former. 



Genus Gladonia, — On the other hand, as a general rule, the same 

 green or yellow colours developed in the Cladonice did change, sooner 

 or later, into red or brownish-red of some shade. On reexamining, 

 several days or weeks after their first testing, the specimens in my 

 herbarium, or in various published fasciculi, to which I had applied 

 potash, I found both paper and plant bearing stains that were 

 sometimes blood-red^ though more frequently brownish-red. The 

 marks on the podetia, or folioles, that had previously been green, 

 were now of a distinct red hue. Sometimes the tint was more of 

 a tawny yellow ; and in some cases a deep fulvous tint was natural, 

 e, g. in deformis. The transition to red did not occur in every 

 case, nor was it always well marked. The same result which 

 was In these cases effected by time, could be, frequently at least, 



