in orchil and litmus, there is a corresponding white one, producible by the action of sulphuretted hydrogen, &c.; and, in proof of this theory, he mentions having obtained from Azolitmine and Betaorceine colorless bodies, to which he gave the respective names of Leuco-litmine and Leuco-orceine.

The author then gave a short summary of Dr. Westring’s experiments on the dyeing powers of the Swedish lichens, which he found might be conveniently divided into four classes, according to the degree of heat employed in their maceration, viz.:—­

    1.  Lichens, whose coloring matter was easily extractable by cold
    water alone.

    2.  Those which required for the elimination of their coloring
    matter, maceration in tepid water (i.e. below 258 degs.  Swedish
    thermometer).

    3.  Those which required maceration in warm water (i.e.between 50
    and 60 degs.  Swedish thermometer).

    4.  Those requiring boiling water alone, or with the aid of
    solvents.

“It must be admitted that our knowledge of the true nature of the colorofic and coloring principles of the lichens is, as yet, very imperfect and confused, and one great cause of the dubity and obscurity overhanging the subject, is the 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