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exceptions to their constancy, some of which were pointed out by Tuckerman 
in a paper in the Am. Nat., April, 1868. It is possible that a lichen may 
possess different chemical constituents at different stages of growth, or under 
different conditions of soil, climate, etc. Experiment on the same plant at 
different periods of its development is necessary to confirm the deductions 
from simple examination. Still, the reactions appear to be constant in most 
of the species of Parmelia and may serve as an aid in their determination, 
while the exceptions remain to be accounted for. Where there appears to be 
an exception we may best say that perhaps the specimen belongs to a dis- 
tinct species.’’ 
Prof. Albert Schneider, in his Text Book of Lichenology, 1897, says of 
chemical reactions: “For some years the chemical behavior of lichens to 
certain reagents has been considered of great importance in delimiting spe- 
cies. After careful testing I have finally decided to abandon the use of these 
reagents since they are practically valueless for the purpose recommended. 
That there are marked chemical reactions cannot be denied : for example, 
the blue Iodine reaction of the thecial wall of the majority of lichens. This 
reaction is, however, so general in its occurrence that it cannot possibly be of 
any value in establishing species, and the coloration varies in different indi- 
viduals of the same species, or even of the same plant at different periods of 
development. The same may be said of the other reactions as those with 
solutions of potassium-hydrate and calcium hypochlorite. That these reac- 
tions should be unreliable is evident when we consider the life history of lich- 
ens; different individuals of one and the same species may develop on 
substrata of widely different composition. These chemically different sub- 
stances adhere to the lichens, and some soluble constituents are also taken 
up by the fungal symbiont which accounts for the difference and unreliability 
of the chemical reactions. 
Prof. Bruce Fink, in his Presidential address to the Iowa Academy of 
Sciences, pays his respects to the subject through an allusion to Dr. Nylander- 
He says: “ Nylander was doubtless too much given to species making, and 
it is unfortunate that he depended too much on chemical tests in his determ- 
inations.” A few pages further on Fink, in alluding to Tuckerman’s ex- 
pressed opinion of theunreliable nature of cnemical tests adds, thatsuchis “a 
view which I suppose meets the approval of latef lichenists generally, since 
we have reached more definite knowledge regarding the anatomy of these 
plants.” In another paper presented before the same Institution entitled, 
“ Notes on American Cladonias,” Prof. Fink says, “ as to chemical tests it is 
extremely doubtful whether they are of diagnostic value in any lichen.” The 
writer will add to these excerpts of American opinion on chemical tests, the 
information communicated by Prof. W. G. Farlow, of Harvard University* 
that Tuckerman “never changed his opinion in later years with regard to use 
of chemical tests in distinguishing species of lichens. He did not consider 
that species could be distinguished in that way.” 
To summarize the foregoing expressions of opinion is to assort belief into 
two groups. Schneider and Fink are associable in the first, for both repu- 
