It is a matter of regret that Greville should have so entirely ignored lichens in his great work on _Scottish Cryptogams_[99]. The two species of Lichina are the only ones he figured, and these he took to be algae. He[100] 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[101] contributions to Smith’s _English Flora_ and Taylor’s[102] 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[103] in his important work _Lichenographia Europaea_ more or less followed his distinguished 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. Fée[104] published an Essay on the Cryptogams (mostly lichens) that grew on officinal exotic barks; Flörke[105] took up the difficult genus _Cladonia_; Wallroth[106] also wrote on _Cladonia_; Delise[107] on _Sticta_, and Chevalier[108] 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[109] 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 “morphosis” 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.