869 



live organs and their contents, since the discovery of the lichen-phy* 

 tozoa (the spermatia, or spermogoni, of" various recent authors). 



" For the purpose of informing myself on their general and special 

 anatomy, I began a detailed microscopic examination of all the Bri- 

 tish genera, subsequently extending my investigations to species ; but 

 this being a labour of immense extent, in a path as yet comparatively 

 untrodden, and requiring therefore a great amount of time and appli- 

 cation, 1 have been unable to work far in this direction. 



" c. Their chemical composition, as ascertained by analysis. A 

 few of the lichens best known to us, on account of their uses in medi- 

 cine and the arts, have, at different times, been analyzed by Berze- 

 lius, Proust, John, Nees. von P^senbeck, Schnedermann, Knop, Her- 

 berger, and other chemists ; but their results have been very discrepant. 

 It is therefore very desirable that the analyses made by these gentle- 

 men should be carefully repeated at the present day, by men experi- 

 enced in botany, as well as in chemistry ; and it is further desirable 

 that we should have an extensive and accurate series of analyses of 

 all the British lichens (or, at least, of as many as can be obtained in 

 quantity sufficient to subject to experiment) before we can come to 

 any general and useful conclusion on the subject. I am not yet suffi- 

 ciently acquainted with practical chemistry to undertake such analy- 

 ses ; but I have had, on different occasions, the ash of a few common 

 species analysed qualitatively by more experienced friends. My 

 efforts, however, in this direction have been greatly circumscribed by 

 want of specimens. It can only be by the analysis of a large number 

 of species that we can accumulate a mass of facts from which we may 

 deduce general principles, and discover how far the chemical compo- 

 sition of different lichens is similar or varies ; whether any, and what, 

 relation subsists between their composition and external appearance, 

 &c. 



" d. Their products and secretions, including the chemistry of their 

 nutritive and pigmentary principles, and its practical application. The 

 subject of the colorific and colouring principles of the lichens has, 

 within the last few years, attracted a due share of that attention which 

 has been increasingly devoted to organic chemistry. Since 1830, Hee- 

 ren, Kane, Schunck, Rochleder, Heldt, Knop, Slenhouse, 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 pub- 

 lished can be implicitly relied upon, and before we can have safe data 



