30 



soil, or when too closely crowded, can a profuse development of 

 lichens have an injurious effect. 



Of the systematists of this period we will mention only Crombie. ' 

 In his classification of British lichens this writer has adopted Ny- 

 lander's system. He does not recognize Schwendener's theory 

 and divides the lichen-algae into gonidia, gonimia and gonidimia. 

 His diagnostic terminology is that peculiar mixture and combination 

 of English and Latin so much employed by English systematists of 

 this as well as of the preceding period. 



We shall conclude this historical. review with a brief reference to 

 fossil lichens ; so far there is no reliable record of any such remains. 

 There is, however, little doubt that lichens existed during former 

 geologic ages. No records are left for the same reason that we have 

 few authentic records of fossil algae and fungi, that is, lichens are 

 not sufficiently resisting to become fossilized. Excavations of pre- 

 historic cave dwellings (Germany) have revealed the presence of 

 lichens (Cladonia rangiferina} among the bones of various animals 

 and the stone implements, which would indicate that man of that 

 early period had already made some economic uses of them. 



1 Crombie, British Lichens, I., 1895. 



