30 



this portion of the subject are contained in various botanical publi- 

 cations. Leigh ton has published a Lichen Flora of Great Britain, 

 but it cannot be said that it is likely to be of much use to the Amer- 

 ican student. Koerber, Sy sterna and Parerga is the fullest German 

 work. Montague's Sylloge contains descriptions of many exotic 

 Lichens. Hepp's Abbildungen gives valuable drawings of spores ; 

 and finally, Krempelhuber's Geschichte der Lichenologie gives an 

 encyclopaedic view of the entire History and Literature of the sub- 

 ject. The fullest lists of works on Lichens for sale are contained, 

 in the catalogues of Freidlander of Berlin, which are furnished by 

 B. Westermann & Co. of New York. 



There are collections of Lichens at Harvard College, the Boston 

 Society of Natural History, Columbia College, the University of 

 Pennsylvania, the National Museum at Washington, and perhaps at 

 other institutions. But I cannot give any detailed information about 

 them. 



CHAPTER V. 



THE AKEANGEMENT QF NORTH AMERICAN LICHENS. 



We conclude our work with a summary of the arrangement of 

 North American Lichens according to Tuckerman's System. Our 

 Lichens are divided into two series and five Tribes, based on the 

 characters of the Apothecia. Families are based on characters of 

 the thallus or apothecia. Spore colors are made the basis of Ge- 

 nera only as they are considered as typically colored or colorless. 

 Other differences are regarded as only gradal, and serve for sub- 

 ordinate divisions. The Collemacei, a separate class with pre- 

 vious writers, are here included in the first Tribe. A peculiar nota- 

 tion is used in the arrangement of closely related plants, and in 

 what follows, those following the leading species are mentioned as 

 subspecies, although that term is not strictly appropriate. Much 

 importance is attached to Habit, but little or none to the Spermatia 

 and to chemical reactions. 



Series I. GYMNOCARPI, with normally open apothecia, and 

 including the first four Tribes. 



Tribe I. PARMELIACEI. Apothecia with a thalline exciple 

 (scutellseform), with now an included proper exciple (zeorine.) 



Fam. 1. UsNEEi. Thallus fruticulose, rarely foliaceous. 



