AS A SPECinC CHARACTEB IN LICHENS. 47 



* 



however, I have long been convinced it cannot be relied upon*. So 

 long ago as 1840, Professor vonMohl publishedf " Einige Beob- 

 achtungen liber die blaue Farbung der vegetabilischen Zellen- 

 membran durch lod/' containing reference to its applications in 

 lichen-histology. The novelty of the present application of iodine 

 consists, as in the cases of bleaching-solution and potash, in its 

 supposed utility as furnishing a '^ character" in the diagnosis of 

 species — a utility which, in all the cases in question, we shall pre- 

 sently see is only supposed ! 



Nylander recommends the application of the reagents he em- 

 ploys to the thallus or apothecia guttatim^ by means of a glass 

 stirrer. But there is frequently great difficulty, except in the 

 single case of potash, of causing their adhesion to, or absorption 

 by, the lichen-tissues. It is generally necessary to make repeated 

 applications of the reagent, aiding the moistening of the lichen 

 by friction. In the case of bleaching-solution, considerable fric- 

 tion is usually necessary, in order to the development of reaction 



friction sufficiently forcible to break up the cortical tissue and 

 expose the medulla. I have found it most convenient first to 

 thoroughly moisten the lichen-thallus with a large drop of the 

 reagent, and subsequently to break up the cortical tissue and ex- 

 pose the medulla under the fluid so applied. 



The reagents before mentioned, applied as I have just described, 

 have yielded me, inter alia, the following colour-results with dif- 

 ferent genera and species of Lichens : 



I. Reaction taith BleacTiing- Solution. — In some cases it bleaches, 

 in others darkens, in others modifies, the colour of solutions of 

 lichen- colouring-matters, these reactions depending in great 

 measure on the amount or strength of the reagent employed. 

 Most of the pale yellowish-green or greenish-yellow infusions are 

 bleached or lightened in colour ; while of those which are brown- 

 ish red, reddish brown, yellowish brown, or brownish yellow, some 

 are darkened, but none are lightened, in colour. 



Genua Boccella, — As already stated, I examined specimens 

 from most parts of the world in which the genus grows, applying 

 the reagent frequently to different parts of the same specimen. 

 I found the reaction, where it occurred at all, immediate, and 

 most vivid at first — a circumstance fully explained in my experi- 



* Vide paper on "Parasitic Micro-lichens*' in Quart. Joum. Micro. Sc. 



January 18C9. 



t In the ' Flora ' (Eegensburg). 



