USES OE LICHENS. 



81 



which is also found in the Dahlia, Elecampane, and other 

 phanerogamous plants ; the former exists more or less abun- 

 dantly in all Lichens, the latter to a limited extent only in 

 certain species. Lichenin may be considered intermediate 

 in composition and characters between the substance termed 

 dextrine and common starch; in different species it occurs 

 forming the walls of certain cells, it lines their interior, or 

 it constitutes the basis of the cell-contents or intercellular 

 substance. Diluted and boiling sulphuric acid convert it 

 into sugar, while nitric acid transforms it into oxalic and 

 saccharic acids. Inuline, which has been detected in Cetraria 

 Islandica, may be regarded as intermediate between common 

 starch and sugar ; so that the two forms of starch occurring 

 in Lichens fill up gaps in the series of the four chief che- 

 mical substances which enter into the composition of the 

 tissues of plants, viz. Cellulose, Starch, Dextrine, and Sugar. 

 Various common species have long been known to yield a 

 gum similar in properties to gum-arabic, for which it has 

 been recommended as a substitute ; such species are Rama- 

 Una fraxinea, Parmelia ceratoph/Ua var. pliysodes, &ndPky- 

 scia prunastri. One of the projects of the late ingenious 

 Lord Dundonald was to apply this gum to calico-printing. 

 The saccharine principles found in minute quantity in some 



G 



