103 



the last quarter of a century, or since the time of Schwendener's 

 epoch-making investigations. All older systems are wholly inade- 

 quate in the light of modern lichenology and for that reason must be 

 discarded. 



As already indicated (see Individualism) lichens form a distinct 

 class of plants having a polyphyletic origin (see Polyphyletic Origin 

 of Lichens). The question now arises, what subdivisions shall be 

 made of this class? After careful consideration it was found that 

 an arrangement into orders, families, genera and species without 

 further subdivision was most natural and useful. We shall now 

 discuss the characters selected for limiting these groups. 



Order Characters. The chief character to be considered in estab- 

 lishing orders is the method of spore-formation. All the known lichens 

 can according to this be arranged in three orders, Ascolichenes, 

 Basidiolichenes and Gasterolichenes. In the order first mentioned 

 the spores are formed in spore-sacs by a process of free cell-forma- 

 tion ; in the second, the spores are formed exogenously by the ab- 

 striction of the ends of specialized hyphas ; in the Gasterolichenes 

 the spores are formed exogenously on basidia within specialized 

 cavities. Only Ascolichenes occur in our territory. It may also 

 be mentioned that the Basidiolichenes l are southern and that the 

 existence of Gasterolichenes' 2 is questioned by some authors. 



The following are some of the groupings adopted by various 

 lichenologists and which are still in use but which are unscientific 

 and therefore untenable. Such are the groupings into homoeomerous 

 and heteromerous ; into gelatinous and nongelatinous ; into crus- 

 taceous, foliose and fruticose ; according to the nature of the algae 

 (gonidia), into Archilichenes, Sclerolichenes, Phycolichenes, Gloeo- 

 lichenes, Byssolichenes and Nematolichenes ; into Pyrenolichenes 

 and Discolichenes. These and other subdivisions which have the 

 significance of orders or sub-orders are not to be recommended, be- 

 cause they add to the existing confusion. It would be impracticable 



'The following authors have thoroughly discussed the Basidiolichenes : 

 Mattirolo, O. Contribuzioni allo studio del genera Cora Fr. Nuovo Giornale 



Botanico Italiano, 13: 245-267. iSSi. 



Johow, P. Die Gruppe der Hymenolichenen. Jahrb. wiss. Bot. 15: 361-409. 



1884. 



2 The Gasterolichenes are discussed by the following authors : 



Berkeley, J. M. Introduction to Cryptogamic Botany, 340. London, 1857. 



Massee, G. On Gasterolichenes, a new Type of the Group Lichens. Trans. 



Royal Soc. London, 178 : 305-309. 1887. 



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