40 



peculiar to lichens 1 ) is typically red, but through impalpable grada- 

 tions, and with increasing induration, it passes into rufous, fusees- 

 cent, and nigrescent; the same species, and even the same indi- 

 vidual, often going through the whole series. Exceptions, indeed, 

 there are, and so normal, that they afford distinctive characters; 

 but all are, notwithstanding, reducible without difficulty to the type. 

 The color of the thallus without doubt tempers that of the disk, es- 

 pecially if this be extenuate and immediately margined by the thal- 

 lus. In this way, and perhaps particularly by extenuation, we have 

 the expallent disks of Usnea and Ramalina, an effect produced, also, 

 in other species by moisture, as in Biatora vernalis. Usnese and 

 Ramalinffi do occur with reddish disks, which color appears also 

 in the cephalodia when they are present Black generally is pecu- 

 liar to the genera that approach the fungi; red to the central and 

 higher groups. 



Besides the above, we have now to add a few words of those wholly 

 foreign colors, with which many individuals occur so imbued, that 

 the normal hue is altogether destroyed. Meyer has treated this at 

 large (Entwick. p. 60, &c.), and Fries more briefly, as follows. To be 

 first mentioned are those accidental colors dependent on inorganic 

 oxides, the effects of which have been placed beyond doubt both by 

 direct experiment and by observation. To the oxide of iron are 

 referable all red and ochraceous-ferruginose crusts, occurring so 

 commonly in our mountainous and alpine districts; to the oxide of 

 manganese., according to Meyer, those which are roseate and pur- 

 purascent; and to the carbonate of lime those chalky- white crusts 

 so common on calcareous rocks, wherein, also, the thallus more often 

 appears in an atypical amylaceous state. Next we have the colors 

 produced by parasitical Byssi, which infest especially the corticoline 

 lichens, and occasion various shades of red. Lastly, lichens are 

 sometimes tinged by the exuding sap of trees, and hence acquire a 

 rufo-fuscous hue. 



Auct. de Chrosi : Fries, Lichenogr. p. 1 05 ; Meyer, Entwick, p. 60 ; 

 Wallroth, Naturgesch. der Flecht. II. pp. 45,417 ; Eschwciler, Syst. 1, c. 



VI. CHRESIS. 



Having thus explained the beginning of the life of lichens, and 

 the progressive development of their vegetative and fructificative 

 organs; having, moreover, presented a view of their principal ana- 

 morphoses, and finally of their colors, we come now to the history 

 of these plants as objects firstly of use, secondly of study, and lastly 

 of systematic arrangement. 



Lichenes are, of all other cryptogamous plants, the most remark- 

 able for their manifold and various uses in technology and medicine, 

 no less than in the economy of Nature, and thence generally of Man. 

 In what follows I have availed myself of all the authorities within my 

 reach, disposing the whole as respecting, I. the Economy of Nature; 

 II. of Man, generally ; and III. particularly, and in the Arts. 



Of the first of these heads very little is satisfactorily known. 



i Gotting. Gelehrt. Anzeig. 1830, No. 141, Fries, 1. c. p. xxxvi. 

 V 



