DR LAUDER LINDSAY ON NEW LIOHENICOLOUS MICRO-FUNGI. 525 



generally assumed to be, but on insufficient grounds, lichenine ; (2.) The asci ; 

 (3.) The sporidia; (4.) The medullary or other tissues of the thallus. Excep- 

 tionally colour-reaction may occur in other tissues. I have, for instance, met 

 with a blue reaction from iodine in the interior structure of the spermogonia 

 of Abrothallus oxysporus (Birnam, June 1856). The commonest iodine-reaction, 

 that with which lichenologists have to do as a botanical character, is that of the 

 hymenial gelatine* in which are imbedded the asci and paraphyses ; and of the 

 asci themselves, on which the reaction is generally the most intense. Typically 

 this reaction is a beautiful Prussian-blue ; that is to say, it has been generally 

 regarded by continental lichenologists as what Nylander calls a " Nota 

 lichenosa," — a diagnostic " character" of lichens as contra-distinguished from 

 fungi. But this blue is not always exhibited in different specimens of the same 

 species, nor even in the same specimen at different times ; it may, moreover, be 

 faintf or fugacious. In a large number of lichens, instead of blue, the colour- 

 reaction with iodine is violet, red, brown, or yellow ; while in another large group 

 there is no colour-reaction! Thus, in the genus Verrucaria, as defined by 

 Nylander (in his " Lich. Scand." p. 266), iodine developes in the hymenial 

 gelatine of 



(a.) One section — -the supposed typical or lichenic reaction. 



(b.) In another section — a wine red. 



(c.) In a third section — a faint bluish or reddish tinge. 



(d.) In a fourth section — no reaction.:): 

 To which it may be here added, that some Verrucarice have no paraphyses, while 

 in others they are distinct ; but are always (where they exist) more or less 

 graceful, delicate, and filiform. Further, different tissue-constituents of the same 

 lichen, or different parts of the same organ, give frequently different colour- 

 results with the same reagent. 



These irregularities in colour-reaction may be conveniently and sufficiently 

 illustrated by the following selection of quotations from the record of my micro- 

 scopical examination of the lichens contained in the published Fasciculi of Scelerer 

 (Switzerland), Nylander (France), and Leighton (England). The advantage of 

 using published Fasciculi is, that a standard of comparison is secured accessible 



* The terra, " gelatine" or " mucilage," is here used, and by lichenologists generally, in a popular, 

 not in a strictly chemical, sense; for it has already been shown that the so-called " gelatine" may 

 really be a form of starch or gum, or a mixture of forms of either or both ! Compare Arthonia 

 melaspermella, p. 283. 



| It is faint or obscure in the following, and in many other, true lichens : — 

 Gollema turgklinn, Schaer. Exs. 433. Asci. 

 Stereocaulon condensatum, Schser. Exs. 509. Asci. 

 Calicium stigonellum, Leight. Exs. 22G. Asci. 



Lecidea Wahlenhergiana v. truncigena, Ach., Leight. Exs. 123. Hymenium, mere trace. 

 J In his "Prodromus" he describes some species as possessing a yellow reaction, e.g. V. an/Una 

 (p. 191). 



VOL. XXV. PART II. 6U 



