174 PARMELIA MILLANIANA. 



After this treatment the hympnial gelatine, or that substance as 

 now modified, revealed a vivid blue instead of the vinous red, which 

 is the usual re-action as stated by authors. 



2nd — The presence of paraphyses, or what may be reckoned 

 equivalent to such, is only revealed after the chrysophanic acid has 

 been dissolved out; in fact, in the specimens quoted, to such an 

 extent was this acid developed that neither thecee, spores, nor any 

 distinctive part of the hymenium were discernible. Different rela- 

 tive quantities of this acid may, and do, exist in different specimens, 

 clouding more or less the hymenium ; hence the discrepancies of 

 writers, as quoted by Mr. Leighton, in their statements of the 

 appearances presented by the hymenium. 



In every instance of Arthonia lurida that has come under my 

 observation, the presence in abundance of distinct and definite 

 branching fibres has been revealed by the process explained above, 

 and not only so, but they may also be seeir more regularly disposed 

 in the sub-hymenial spaces. It is scarcely necessary to say that 

 the presence of these fibres in the hymenium determined me to 

 classify the lichen in question with the Lecidese under the name of 

 L. emphysa, and that it was only when authentic specimens of A. 

 lurida revealed identical phenomena that I was constrained to revert 

 to the genus Arthonia ; whether this and one or two othei- species 

 are still entitled to rank with the Arthonia^ is another question. 



The coerulescent tint assumed under the action of iodine, by the 

 gelatine not dissolved out by the potash, and which, accordingly, 

 is presumably of a different constitution from the general gelatinous 

 mass, has also been developed in every instance: 



As hinted at in my remarks under A. lurida, I have detected 

 similar phenomena in two or three others of the same genus ; but 

 I deemed it prudent to defer further consideration of the subject 

 until a more extended series of experiments had either defined the 

 limits of such a section, or disproved the existence of any such. 



I may not, as Mr. Leighton suggests, know A. lurida, or rather 

 the group of forms that may be said to constitute that species. I 

 certainly have not dissected, as he has done, several hundred speci- 

 mens of it, but I have examined pretty minutely several, and 

 amongst them specimens from Dr. Nylander, as well as from one or 

 two other continental botanists. Notwithstanding this it may be a 

 matter of regret that, previous to the determination of Lecidea 

 emphysa, I had not secured genuine specimens of A. lurida from 

 Mr. Leighton. 



JAMES STIRTON. 



The Editor has permitted me to peruse the MS. of Dr. Stirton's 

 courteous and gentlemanly reply to my remarks on his P. Mil- 

 laniana, and has suggested the desirability of my addiug,a note to 

 that communication in the present number. But all that I can 

 Bay on the subject is simply to repeat that the sterile thallus which 



