53 DR. LAUDJEIt LINDSAY ON CUEMICAL REACTION 



effected at once by a subsequent application of polasli, and less 

 frequently by ammonia. The latter reagent, on second applica- 

 tion after a varying interval of time, sometimes left a permanent 

 greenisli-yellow in cases wliere potash produced a blood- or crim- 

 son-red. In other cases the second application of ammonia im- 

 parted a brownish tinge to the original greenish -yellow reaction* 

 The secondary development of red or brown tints, however, was 

 commoner with potash. The depth of the red colour appears, 

 frequently at least, to be proportionate to the brilliancy of the 

 previous lemon-yellow ; and it is therefore most inarked on thd 

 folioles, especially when they are white and mealy, e. g, in some 

 forms of squamosa. Potash here developes various beautiful 

 shades of green and yellow, which change (or not) afterwards to 

 various shades (sometimes beautiful and deep) of red, the same 

 reaction being obtained by a second addition of potash or am- 

 monia. 



It has appeared in my experiments that Cladonicd which have 

 red apothecia generally give a secondary red reaction with potash, 

 while those with hroivn apothecia do not (e. g. aggregata^ furcata^ 

 gracilis). This may be a mere coincidence ; at all events it is as 

 yet a doubtfully correct generalization. 



The transience of the green colour in Cladonia is in contrast 

 with its (at least comparative) permanence in Parmelia^ Fliyscia^ 

 Lecanora^ Lecidca^ JJrceolaria^ Tlilyctis^ LecanactiSy and Arihonia. 



No reaction occurs when the thallus, especially the podetia, is 

 brown or dark-coloured, <?. g, in forms oi furcata. Brown apo- 

 thecia arc also unaffected by potash. Eeaction is always obscure 

 or faint iii old specimens ; so that the intensity of colour de- 

 veloped depends, greatly at least, on the age or freshness of the 

 Bpecimen operated on. Hence the specimens in Schserer's Exsic- 

 cati gave a reaction which was either not perceptible or not 

 vivid. Even the heightening of the natural greenish-yellow 

 colour of the ])lant was in these cases rare. 



The greenish-yellow reaction is most vivid where the thallus Is 



F 



w^hite, grey, or pale ; it is deepest generally on the folioles of the 

 horizontal thallus, especially where it is microphylline and ste- 

 rile, e. g. in var. erratica of degenerans, from Otago. The podetia 

 and folioles or squamules sometimes give different reactions, at 

 least as to shade or intensity of colour. The same differences are 

 exhibited in different specimens of the same species, according 

 to the conditions of growth or preservation, e.g. in retipora. 



