PERIOD V. 1803-1846 13 



Lichina are the only ones he figured, and these he took to be algae. He' was 

 well acquainted with lichens, for in the Flora Edinensis he lists 128 species 

 for the Edinburgh district, arranging the genera under "Lichenes" with the 

 exception of Opegrapha and Verrucaria which are placed with the fungus 

 genus Poronia in " Hypoxyla." Though he cites the publications of Acharius, 

 he does not employ his scientific terms, possibly because he was writing his 

 diagnoses in English. Two other British works of this time still remain to 

 be chronicled : Hooker's^ contributions to Smith's English Flora and 

 Taylor's' work on lichens in Mackay's Flora Hibernica. Through these the 

 knowledge of the subject was very largely extended in our country. 



The classification of lichens and their place in the vegetable kingdom 

 were now firmly established on the lines laid down by Acharius. Fries* in 

 his important work Lichenographia Europaea more or less followed his dis- 

 tinguished countryman. The uncertainty as to the position and relationship 

 of lichens had rendered the task of systematic arrangement one of peculiar 

 difficulty and had unduly absorbed attention ; but now that a satisfactory 

 order had been established in the chaos of forms, the way was clear for other 

 aspects of the study. Several writers expressed their views by suggesting 

 somewhat different methods of classification, others wrote monographs of 

 separate groups, or genera. F^e* published an Essay on the Cryptogams 

 (mostly lichens) that grew on officinal exotic barks; Florke" took up the 

 difficult genus Cladonia;^ ?L\\xo\h'' also wrote on Cladonia; Delise* on Sticta, 

 and Chevalier" published a long and elaborate account of Graphideae. 



Wallroth and Meyer at this time published, simultaneously, important 

 studies on the general morphology and physiology of lichens. Wallroth" 

 had contemplated an even larger work on the Natural History of Lichens, 

 but only two of the volumes reached publication. In the first of these he 

 devoted much attention to the " gonidia " or "brood-cells" and established 

 the distinction between the heteromerous and homoiomerous distribution of 

 green cells within the thallus; he also describes with great detail the "mor- 

 phosis" and "metamorphosis" of the vegetative body. In the second volume 

 he discusses their physiology — the contents and products of the thallus, 

 colouring, nutrition, season of development, etc. — and finally the pathology 

 of these organisms. He made no great use of the compound microscope, 

 and his studies were confined to phenomena that could be observed with a 

 single lens. 



Meyer's" work contains a still more exact study of the anatomy and 

 physiology of lichens; he also devotes many passages to an account of their 

 metamorphoses, pointing out that species alter so much in varying conditions, 

 th^t the same one at different stages may be placed even in different genera; 



' Greville 1824. ^ Hooker 1833. " Taylor 1836. * Fries 1831. ' Fee 1824. " Flbrke 1828. 



' Wallroth 1829. * Delise 1822. '^ Chevalier 1824. " Wallroth 1825. " Meyer 1825. 



