AS A SPECIFIC CHAHACTEB IN HGIIENS, 57 



r 



There may be no reaction in one part of the same specimen 

 which in another yet exhibits the typical yellow reaction, e. g 

 retipora. All conditions of reaction — absence, obscurity, or in- 

 tensity — rinay occur in different forms or conditions of the same 

 species, e. g. pyxidata. Eeaction, where it is developed at all, is 

 immediate. The developmeut of yellow is commoner with ammo- 

 nia than with potash. 



" The application of both the reactives " (potash and bleach- 

 ing-solution), says Leighton, " enables us to distinguish more 

 accurately and readily the different species which have been here- 

 tofore comprehended under the name rangiferina *' * (p. 119). 

 "True or typical" 0, rangiferina has, according to him, the reac- 

 tion K+ C — ; <7. sylvatica^ Hffm.,has Kf t+ C + ; var. alpestrisj 

 Sell., he refers to C. sylvatica, with the reaction Kf+ C+ ; while 

 2)umila, Del., is a form only, also referred to C, sylvatica^ and also 

 having reaction Kf+ C + . C, pycnocJada has the double nega- 

 tive reaction K — C — . As already mentioned, I made a special, 

 examination of the forms of 0, rangiferina and its allies, of which 

 my herbarium possess.es a considerable suite of specimens both 

 from foreign and home stations. The result was this, that, even 

 in the ordinary form of (7. rangiferina^ as determined by Mudd, 

 potash produced in some cases a distinct greenish-yellow, while in 

 others there was no reaction. In some cases the said greenish- 

 yellow was intensified by bleaching- solution, in others it was un- 

 affected, while in a third group it was decolorized. Generally no 

 effect was produced by bleaching-solution on old stains made by 

 potasli some months previously ; which stains were frequently 

 reddish-yellow or reddish. The same phenomena were observed in 

 CI, pycnoclada from New Zealand. Moreover, in general terms, 

 the same reactions occurred in sylvatica, alpestris, and the type, 

 I therefore regard chemical reaction in these and such cases as 

 utterly useless, or misleading, in diagnosis. Notwithstanding the 

 supposed distinctions indicated by Leighton and Nylander, I still 

 hold to the opinion thfit sylvatica, alpestris, pycnoclada^ with their 

 allies, may with propriety be referred to the single type 0. rangi- 

 ferina J, 



b I 



w 



4 



* Ann. Nat. Hist. 1867, vol. xix. 



t I am not aware what distinction Leighton draws between K and Kf. 



X Observations on the confusion between varieties and species In the genus Cla- 

 donia wiU bo found in the author's paper " On Arctic Cladxmim:' Trans. Bot 

 Soc. of Edinb. 1867. vol. ii. pp. 169. 175, 178. 



