American lichenologists were also extremely active all through this period. The comparatively few lichens of Michaux’s[113] _Flora_ grouped under “Lichenaceae” were collected in such widely separated regions as Carolina and Canada. A few years later Mühlenberg[114] included no fewer than 184 species in his _Catalogue of North American Plants_. Torrey[115] and Halsey[116] botanized over a limited area near New York, and the latter, who devoted himself more especially to lichens, succeeded in recording 176 different forms, old and new. These two botanists were both indebted for help in their work to Schweinitz, a Moravian brother, who moved from one country to another, working and publishing, now in America and now in Europe. His name is however chiefly associated with fungi. Later American lichenology is nobly represented by Tuckerman[117] who issued his first work on lichens in 1839, and who continued for many years to devote himself to the subject. He followed at first the classification and nomenclature that had been adopted by Fée, but as time went on he associated himself with all that was best and most enlightened in the growing science. Travellers and explorers in those days of high adventure were constantly sending their specimens to European botanists for examination and determination, and the knowledge of exotic lichens as of other classes of plants grew with opportunity. Among the principal home workers in foreign material, at this time, may be cited Fée[118] who described a very large series on officinal barks (_Cinchona_, etc.) so largely coming into use as medicines; he also took charge of the lichens in Martius’s[119] _Flora of Brazil_. Montagne[120] named large collections, notably those of Leprieur collected in Guiana, and Hooker[121] and Walker Arnott determined the plants collected during Captain Beechey’s voyage, which included lichens from many different regions. G. PERIOD VI. 1846-1867 The last work of importance, in which microscopic characters were ignored, was the _Enumeratio critica Lichenum Europaeum_ by Schaerer[122], a veteran lichenologist, who rather sadly realized at the end the limitations of that work, as he asks the reader to accept it “such as it is.” Many years previously, Eschweiler[123] in his _Systema_ and Fée[124] in his account of _Cryptogams on Officinal Bark_, had given particular attention to the internal structure as well as to the outward form of the lichen fructification. Fée, more especially, had described and figured a large number of spores; but neither writer had done more than suggest their value as a guide in the determination of genera and species.