fact that different
analysts have arrived at most opposite results, even in the
examination of the same species. For instance, in _Rocella
tinctoria_, which has, of all the dye-Lichens, been most frequently
selected for analytical investigation, on account of its important
product orchil, the discrepancies between the results obtained are
very striking. In it Heeren discovered his _Erythrine_; Kane his
_Erythriline_; Schunk his _Erythric acid_; and Stenhouse three
different substances in as many varieties of the plant; all of these
bodies differing more or less from each other in composition and
properties (at least, if we are to assume, as correct, the
descriptions given of them by their respective discoverers").

"I have already hinted that there is no ratio between the external
and internal color or structure of a lichen, and the kind or amount
of coloring matter it will be found to yield. It is exceedingly
natural to suppose that such a ratio should exist; but, proceeding
for some time on this supposition, I was frequently disappointed in
my results--the most showy and brilliantly colored lichens often
furnishing the dullest and most worthless colors. For instance, the
bright yellow thallus of _Parmelia parietina_, and the beautiful
scarlet apothecia of _Scyphophorus cocciferus_, instead of producing
a rich yellow in the one case, and a deep crimson in the other,
yielded, respectively, only dirty greenish-yellow and brownish
colors. As a general rule I should almost be inclined to say that
the finer the color of the thallus of any given lichen, the more is
that lichen to be suspected of poverty in valuable coloring matters;
and that, on the other hand, the palest pulverulent or crustaceous
species, especially such as are saxicolous, may be expected to yield
the most beautiful and valuable pigments (_e.g._ the Rocellas and
Lecanoras). In such circumstances it is necessary to have some test,
of easy applicability, of the kind and amount of colorific
properties of any lichen, and this fortunately is readily
attainable."

The fourth section of the paper was devoted to the consideration of
the various tests of colorific power, which have been recommended by
different authors. "Of these, the greater number proceed on the
principle of developing the coloring matter by some alkali,