AS A SPECIFIC CHAEACTEE IN LICHEKS. 59 



througliout the genus. The reaction is most marked where the 

 thallus is palest and softest, e.g. in Ceylon Orchella-weed [which 

 ^. Montagnei], where the reaction is immediate and the colour 

 deep ; it was most distinct of all in Zambesi Orchella-weed, which 

 is the same form of S>,fuciformis. In the ordinary, non-coria- 

 ceous forms of B. facjformu^ as imported by archil-manufac- 

 turers, I never met with it ; nor was there any reaction in Leigh- 

 ton's Exs. No. 171. The reaction is least distinct where the 

 thallus is dark-coloured, terete, and coriaceous. In B. tinctoria 

 (thickest form) the colour was dull indigo, or absent. In B. 

 phycopsis there was no reaction, or a pale azure was slowly 

 developed. 



This colour-reaction was of no use in any case as a means of 

 diagnosis. 



Leighton says iodine distinguishes SpTicerophoron coralloides 



from S.fragilis^ "a long-desired distinction " (p. 442) — a phrase 



which, if it mean anything, appears to imply his anxiety to 



multiply species by means of minute and trivial differences ! 



I found iodine to produce a blue or violet in the medullary 



tissue of the former lichen, a yellow in the latter. Nevertheless 



my opinion is not influenced to regard them otherwise than as 

 referable to a single type. 



My whole present experiments and inquiry hare led to the 



following general conclusions, or have embraced the following 



general results : 



I. Not only do tlie results obtained by different observers on 

 the same species differ widely, but those of the same observer at 

 different times or in different circumstances do so also. Leigh- 

 ton and Nylander do not always agree. Th. M. Fries differs from 

 both * J while my results are also frequently quite of an opposite 

 character to theirs. Moreover I have found in reexamining 

 the same specimens, that different results have been obtained. In 

 one case a distinct colour-reaction might be obtained, while sub- 

 sequently it was faint or absent. This must have been due, appa- 

 rently, to some trivial difference in the reagent or its application, 

 or in the parts of the same thallus operated on. A difference in 

 the degree of concentration or freshness of the reagent, or in the 

 amount of friction employed, would account easily for all the 

 discrepancies in the results obtained. 



II. Not only do results differ in different specimens, or indivi- 



* Vide the Table of Cladonim given in his ' Lichenes Spitsbergenses/ p. 29. 



