AS A SPECTFTC ClTABACTEIl IK LTCHENS. 45 



examination of the Lichen-tissues, finding it useful in dissolving 

 oily protoplasm and other material which interfered with the 

 clear delineation of cell-nuclei and tube-walls or septa. Thus, in 

 microscopic analysis of the hymenium, I use or used it to render 

 distinct the outlines, or walls and divisions, of cells or tubes that 

 were otherwise obscure, e,g. the paraphyses of AhrotJialltis. The 

 novelty of its application by Nylander and Leighton, as in the case 

 of bleaching-solution, consists in the assertion that its reaction 

 with the cortical layer of the Lichen-thallus may be used as 

 a hofanical character — as a guide, that is, to the classification 

 of species. As in the case of bleaching-solution, the sequel 

 will also show how far this application of the reagent is to be 

 trusted. 



IV. lAquoT AmmonicB, otherwise Solution of Ammonia, the com- 

 moner or weaker solution of Pharmacy. — Ammonia is the most im- 

 portant of all alkalies in relation to the chemistry of the lichen- colo- 

 rific principles and their coloured derivatives, probably on account 

 of its containing and supplying nitrogen ; whilst its importance is 

 fully recognized in relation to the development from lichens of co- 

 lours of the archil class. In experiments with the stirrer on the thal- 

 lus or apothecia, it is inferior in usefulness (if either reagent is to 

 be considered useful) to potash ; while in those on aqueous or alco- 

 holic decoctions containing colorific or colouring-matters in solu- 

 tion, it is as decidedly superior, being of much more general appli- 

 cability. In the latter class of experiments, I have used it largely 

 for 20 years ; and the results were partly made public in my first 

 series of researches on the lichen- colouring-matters. Even at 

 a much earlier date, however, the ammonia test seems to have 

 been applied to the determination of species. In 1858, I met 

 with, in the British Museum Herbarium, a specimen of Cladonia 

 hacillaris, Ach. ( = (7. macilenta, Hffm.), presented by Sir Thomas 

 Gage, and bearing the following label in his handwriting, " This 

 difficult species may be distinguished in all its modifications by 

 immediately turning yellow when touched with volatile alkali." 

 Now Sir Thomas's lichens were mostly from Killarney (Ireland), 

 collected in or about 1810. I believe Sir Thomas to have as- 

 signed much too high a value to this "criterion" or*' character;" 

 but his statement is important as showing that the views of Ny- 

 lander and Leighton are by no means new, whether or not it 

 prove that they are true ! In point of fact, chemical reaction 

 seems to have been not unfrequently recognized by the earlier 



