II 



IV. PERIOD. 



From Weber (1779) to Wallroth and Meyer (1825). 



In the previous periods lichens were classified mainly according 

 to the differences in the form and structure of the thallus. In this 

 period an attempt was made to classify them according to the " fruit- 

 ing," that is, according to the form and structure of the apothecia. 

 The first beginnings of this new departure, of course, commenced in 

 the previous period, as we have already noted. Weber, 1 however, 

 made the first intelligent effort to classify lichens upon this new 

 basis. This author had formerly grouped all lichens in one order 

 under " Cryftogamia ;" he now arranged them under eight genera, 

 Verrucaria, Tubercularia, Sfikaeroceftkalum, Placodium, Lichen, 

 Colletna, Cladonia and Usnea ; of these, the first four were based 

 upon the characters of the apothecia alone ; the others upon the 

 characters of the thallus, as well as those of the apothecia. The 

 majority of Weber's contemporaries adopted this new method of 

 classification, with the result that entirely new systems were formed 

 and new genera established. The following were some of the most 

 active systematists: Willdenow, 2 who discovered the genus Pelti- 

 gera; Schreber, 3 who proposed the genera Physcia, Cornicularia, 

 Sticta and Stereocaidon ; Humboldt, 4 who founded the genus Oj>e- 

 grapha. To Persoon' 5 are credited the genera Calicium, Sfthaero- 

 ■phorus, Baeomyces and Placodium. Although the majority of 

 lichenologists followed in the footsteps of Weber, there were a con- 

 siderable number who could not disengage themselves from the Lin- 

 naean influence. -Of these we will mention only Hagen 6 and Joly- 

 clerk. 7 



The Swedish lichenologist Acharius" began his study of lichens 



1 Weber, G. H. Wigger's Primitiae Florae Holsatiae. Kiel. 17S0. Also, Spici- 

 legium Florae Goettingensis. Gothae. 177S. 



2 Wildenow, C. L. Flora Berolinensis Prodromus. Berolini. 17S7. 



3 Schreber, D. J. C. See Linne's Genera Plantarum, Sth ed., Vol. I. Frankfort- 

 on-the-Main. 1791. 



4 Humboldt, A. von. Florae Freibergensis. Berolini. 1793. 



5 Persoon, C. H. Einige Bemerkungen uber Flechten. Usteri neue Annalen der 

 Botanik, 1 : 1-32. 1794. 



6 Hagen, C. G. Tentamen Historiae Lichenum. Regiomont. 17S2. 



7 Jolyclerk, N. Cryptogamie complete, ou description des plantes, dont les etami- 

 nes sont peu apparantes. Paris. 1799. 



8 Acharius, E. Nov. Act. Reg. Sc. Holmiae, 15: 237-259. 1794. Nov. Act. Reg. 

 Sc. Stockholmiae, 16 : 1795. 



