completed to the beginning of 1897. Other works treating of the 

 history of these plants, notably Lindsay's British Lichens have also 

 been made use of. 



Each period is marked by some special evolutionary progress in 

 lichenology. It must not be supposed, however, that these periods 

 are in reality clearly and distinctly separated. One period gradu- 

 ally merges into the other, which makes the distinction more or less 

 accidental or arbitrary. There are no doubt minds that tower above 



ml 



their contemporaries and whose works are to a certain degree epoch- 

 making ; on closer examination it is found, however, that they have 

 built upon the foundation laid by workers that have gone before. 



Only a few of the more important investigators in lichenology are 

 mentioned. It would be impracticable as well as unnecessary to refer 

 to all the authors who have written on the subject. The publications 

 issued number thousands ; to collect and digest these would be the 

 work of many years. The references cited as footnotes are pri- 

 marily of historic interest. The more important references to 

 works having real scientific value are given on pp. xi-xvii. In order 

 to avoid repetition these are referred to by number, where they 

 are mentioned in the historical review, or in the text proper. 



It is thought most appropriate and convenient to divide the his- 

 tory of lichenology into seven periods, as follows : 



I. Period: From Theophrastus (371-286 B. C.) to Tourne- 

 fort (1694). 



II. Period: From Tournefort (1694) to Micheli (1729). 



III. Period: From Micheli (1729) to Weber (1779). 



IV. Period : From Weber (1779) to Wallroth and Meyer 

 (1825). 



V. Period: From Wallroth and Meyer (1825) to Schwen- 

 dener (1868). 



VI. Period: From Schwendener (1868) to Reinke (1894). 



VII. Period: Beginning with Reinke (1894). 



I. PERIOD. 

 FROM THEOPHRASTUS (371-286 B. C.) TO TOURNEFORT (1694). 



The earliest references to lichens are all more or less unre- 

 liable. There is little doubt that lichens were known, but they were 

 looked upon as mosses, algae or fungi, and classified with these 



