The subject of the colorific and coloring principles of the lichen has, within the last few years, attracted a due share of that attention which, has been increasingly devoted to organic chemistry.  Since 1830, Heeren, Kane, Schunck, Rochleder and Heldt, Knop, Stenhouse, Laurent and Gerhardt, have published valuable papers on these principles; but, here again, we have to regret the great discrepancy in the various results obtained, and there is therefore, here also, imperatively demanded re-investigation and correction before any of the results already published can he implicitly relied upon, and before we can have safe data from which to generalise.  I have no doubt that a great proportion of the obscurity overhanging this subject depends on the circumstance that many of the chemists, who have devoted attention to the color-educts and products of the lichens, were not themselves botanists, and have therefore probably, in some cases at least, analysed species under erroneous names, and also because their investigations have comprehended a much too limited number of species.

Their utility in the arts, and especially in dyeing—­including the collection of a series of the commercial dye lichens, i.e., those used by the manufacturers of London, &c., in the making of orchil, cudbear, litmus, and other lichen dyes.  While investigating the dyeing properties of the lichens, I made experiments, with a view to test their colorific power, on as many species as I could obtain in sufficient quantity, to render it at all useful to operate on—­that number, however, being very limited (between forty and fifty).

Dr. Lindley adds, many parties may be able to aid his investigations, by furnishing information on their economic uses, and on their special applications in dyeing and other arts—­(particularly on their employment, as dye agents, by the natives of Britain and other countries)—­with specimens of the lichens so used, and their common names—­specimens of fabrics dyed therewith—­notes of the processes employed for the elimination of the dyes, &c.  Parties resident in, or travelling through our western Highlands and Islands, the northern Highlands, Ireland, Wales, Norway, Iceland, and similar countries, are most likely to be able to afford this description of information—­many native lichens being still used by the peasantry of these countries to dye their homespun yarn, &c.

He proceeded to treat—­1.  The vast importance of this humble tribe of plants in the grand economy of nature, as the pioneers and founders of all vegetation. 2.  Their importance to man and the lower animals, as furnishing various articles of food. 3.  Their importance in medicine, and especially in its past history, at home and abroad. 4.  Their importance in the useful and fine arts, and especially in the art of dyeing. 5.  Their affinities and analogies to other cryptogamic families, and to the Phanerogamia. 6.  Their value as an element of the picturesque in nature; and, 7.  Their typical significance.

    He then adverted more especially to the subject of his
    communication, under the ten following heads:—­