24 



the Verrucarise of limestone rocks are generally different from those 

 of the granitic. A single fossil lichen, Opegrapha antiqua, Lesq., 

 has been found in Tertiary formations at the west, while eight spe- 

 cies have been observed in Europe. But ours is the only species of 

 which the characters were sufficiently recognizable to enable its 

 genus to be determined. 



As to the number of species on our continent it is impossible to 

 #peak with exactness. It is as yet too imperfectly explored ; and 

 there is besides a great difference of opinion as to what constitutes 

 a species. An estimate made by the writer several years ago gave 

 a little over 800 species, distributed among 75 Genera, within our 

 limits. Of the described species 75 were Arctic, 112 Alpine, 171 

 sub-tropical, and 103 Western. The number of species in New 

 England was 399. But a good many species have since been added 

 in all these regions, and it is likely that more than 1000 species 

 may ultimately be found within our limits. 



CHAPTEE IV. 



THE HISTORY or LICHENS. 



Krempelhuber, in his exhaustive work Geschichte der Lichenologie, 

 divides the History of the Science into six Periods: (1) from the 

 earliest times to Tournefort at the close of the 16th century ; (2) 

 from Tournefort to Micheli, in 1728 ; (3) from Micheli to Weber, in 

 1779 ; (4) from Weber to Acharius, in 1802 ; (5) from Acharius to 

 De Notaris, in 1846 ; (6) from De Notaris to the present time, 

 (which when his work was published was 1867.) 



The first four periods may be passed over briefly. Theophrastus 

 mentions two plants supposed to be Usnea barbata and Roccella 

 tinctoria. Evernia furfuracea has been found and identified in 

 Egyptian coffins, having been well adapted from its softness to fill up 

 the vacant places. But the ancients had no conception of Lichens 

 as a distinct class. The lost work of Solomon, in which were de- 

 scribed all plants from the cedar of Lebanon to the hyssop on the 

 wall, perhaps did not include the Cryptogamia. Several Middle 

 Age writers mention Lichens as '" fucus," " muscus," or " pulmo- 

 naria." About 28 species and forms of Lichens were known in the 

 16th century. Tournefort first distinguished them from the musoi 

 and applied to them the distinctive term Lichen, under whieh all 



