AS A SPECinO CHARACTEB IN LICHENS. 39 



Leighton formularizes what he terms these " very remarkable 

 reactions/' and applies them to the minute discrimination of 

 species and varieties in the complex genus Gladonia. He tests 

 these species and varieties by the double reaction of lime and 

 potash, bis latest formulae being the following : 



K+ C+ = yellow reaction with aqua potassaj, yellow 



heightened by bleaching-solution. 



K+ C— = yellow with aq. pot., this yellow being de- 

 stroyed by bleaching-solution. 



K— C+ = No reaction with potash, but a distinct yellow 



with bleaching-solution. 



K— C— = No reaction with either or both chemicals. 



Leighton writes, " This new mode of testing enables us to dis- 

 tinguish more accurately and definitely the limits of the different 

 species or forms, and appears to afford a more satisfactory con- 

 firmation than that obtained by the application of the hydrate of 



potash alone The value of the chemical tests in furnishing 



us with additional and confirmatory specific characters becomes at 

 once plainly manifest," enabling him, he asserts, to classify 

 properly what Acharius, Turner and Borrer, Ny lander, and other 

 distinguished lichenologists, who had depended on " external cha- 

 racters and aspects alone,*' had failed to effect (p. 100) ! He refers 

 again and again in some form to the " real utility and value of che- 

 mical tests" (p. 100) 



The object of the inquiry and experiments whose results are re- 

 corded in the present communication, was an endeavour to deter- 

 mine whether the phenomena described by Nylander and Leighton 



are so constant as to be entitled to constitute " cAarac/^r^ " of any 

 value in hotanical diagnosis^ on the one hand, and the extent or sense 

 to or in which novelty could be said to attach to the introduction of 

 the tests under review, on the other. I read the papers of these 

 lichenologists with considerable surprise, because their results or 

 assertions are in some measure the reverse of the results and gene- 

 ralizations of a lengthened and careful series of experiments, on 

 the colorific properties of Lichens, made by myself nearly twenty . 



reaction 



scribes depends on the presence of cerUln specified colorific or coloured acids. 



* Not. Lich. No. XII. " On the Cladonici in tlic Ilookerian Herbaritim 

 at Kew" [tested by bleaching-solution and potash], Ann. Nat. Hist. 18G7, 

 vol. xii 



