58 DE, LAUDER LINDSAY ON CHKMICAL EEACTION 



Leighton'a scheme presents, however, other difficulties within 

 itself. For instance, he indicates two forms of Gl. ceratopJiylhy 

 Eschw., one with the reaction K— C— , the other with that of 

 Kf+ C + *; of CI Florheana, Fr., form seductrix, Nyl., he 

 mentions, as a noteworthy matter, that Nylander gives the reac- 

 tion as K+, while he found it the reverse in a specimen in the 

 Kew Herharium, named by Ny lander himself (p. 119). " Dif- 

 ferent reaction/' he also asserts, "separates amaurocrwa and un- 

 cialis^ to say nothing of the different external characters " 

 (p. 120) ! In neither the one nor the other did I find the reaction 

 so distinct as to he worthy of record ; and I do not think the " ex- 

 ternal characters " differ to such extent as to forbid their refer- 

 ence to a single type f, 



III. Meaction of Iodine. — I have elsewhere i shown that the 

 iodine test cannot be depended on as a means of diagnosing X*- 

 cTietis from Fungi §. In true Lichens, applied to the tissues of 

 ihe hymenium, I have met with the following results : — There la 

 frequently a beautiful hlue reaction, embracing various shades of 

 Prussian- or indigo-blue ; in other cases the colour developed is 

 violet^ embracing various shades between blue and red; in a 

 third group the colour-reaction is red^ of various tints : in a fourth 

 it is yellow y which is apparently merely the colour of the reagent; 

 in other words, there is no reaction. Moreover, in the same 

 species under different circumstances, the reaction may be ob- 

 scure, if present, or it may be absent. 



Nylander asserts that the medulla of Soccella Montagnet 

 strikes a blue with iodine. In some cases it does, but in others 

 it does not. I made special study of the reaction of iodine on 

 the medullary tissue in the genus Soccella^ with the following 

 results. In aU the species examined it was variously present or 

 absent. It was absent in fuciformisy Monfagneiy jphycopsisj and 

 tinctoria in certain cases ; while in other specimens of the same 

 species it was present in some form, though frequently faint and 

 slowly developed. As a general rule, it may be said to occixr 



» Ann. Nat. Hist. 1867, vol. xix, p. 112. 



t Nylander (Lich. Scand. p. 59) seems to hold a similar opinion, . 



I *' On Arthonia melaspermella;' Joum. of Linn. Soc. 18G7, Botany, vol. ix* 

 p. 283. 



§ Nylander disclaims any desire to consider Iodine more than an accessory 

 means of distinguishing certain of the lower Lichens from the Fungi ; but I 

 deny that this te^t can in any sense, or with any safety, be accepted as diagnodtc 

 between members of these two great orders. 



