— 70 — 
difficult to believe that the lack of conformity is due to a difference in inter- 
pretation of fact, nor is it thought to be an effect of similar specific lichen 
forms furnishing dissimilar phenomena. A possible explanation may be 
that Willey, under the guidance of Nylander, came to have a better knowl- 
edge of Parmelia species than did Tuckerman, and a more exact conception 
of the things to be recognized in chemical testing. 
The student on first taking up the subject of chemical criteria is apt to 
find it difficult to exactly determine what constitutes a satisfactory test. The 
manuals contain fairly clear directions, but mere words only convey an out- 
line, leaving experience to supply the details. There are some tempera- 
mentally unfitted to make use of the tests, and others, solitary workers, 
without guidance except for the books. Both fail from obvious reasons. In 
their inception chemical tests were only recommended as aids to the char- 
acterization of lichens, and much of the early antagonism to their employ- 
ment is attributed to a misapprehension of their point. In the Annals and 
Magazine of Natural History, 1869, Rev. W. A. Leighton (Not. Lich. XVIII) 
in reviewing Dr. Th M. Fries’ Lichenes Spitzbergenses, takes occasion to 
say, “With much satisfaction we observe that the learned author has over- 
come his prejudice against the application of chemical tests in lichens, and 
has made ample use of them with very satisfactory results. He, however, 
still appears to labor under a misapprehension that the advocates of chemi- 
cal tests wish to inculcate that species may be distinguished by chemical 
means alone (hac sola nota). All that has ever been ascribed to them is that 
they are most useful and indispensable aids as affording confirmatory char- 
acters and in discriminating doubtful or externally allied species. In the 
Cladoniae he has almost uniformly confirmed the results of our own exam- 
ination of the tribe. But it may be well here to correct a doubt which seems 
to exist in consequence of the chemical test producing in certain species a 
slight degree of fuscescence only, by explaining that when the proper reac- 
tion takes place it does so instantly, and that the fuscescence which is in 
some instances observable is not to be regarded as a reaction at all.” 
In the same publication for 1869, Leighton (Not. Lich. XXIX) again writes, 
“ The student is especially warned against misconception as to chemical tests 
constituting a sole specific character. All that has ever been asserted re- 
specting them is that they afford an additional and confirmatory specific 
character. And in those cases where external characters are similar or ap- 
proximate, and doubt necessarily exists, their value as such will be abun- 
dantly apparent.” Leighton then proceeds to quote Jfrom a paper by Dr. 
Nylander, aptly designating the citation as an “ admirable caution.” The 
learned Doctor says: “The analysis of lichens made by chemists often fail 
through the neglect of an exact determination of the species, and probably 
not less often by the mixture of specimens confounded together and incor- 
rectly assigned to one single species. For the chemist no less than for the 
physiologist it is of the greatest importance to know exactly what is the plant 
we have under observation — that is, to have well determined the plant which 
we are studying.” In other words, returning to Leighton, “he must not 
