26 



POPULAR HISTORY OP LICHENS. 



these extreme views, numerous theories were from time to 

 time advanced to account for their discrepancies, or supply 

 their omissions ; but they were all equally characterized by 

 one circumstance, which completely invalidated their sta- 

 bility, viz. that they were unsupported by, or inconsistent 

 with fact. According to the views taken by observers of the 

 relative importance of the vegetative or reproductive organs, 

 systems of classification were based on the characters of 

 the thallus or apothecia ; and as a result in either case, they 

 were unnatural and artificial. By earlier Lichenologists, the 

 characters of the thallus alone were taken as a basis of 

 classification; by their immediate successors, those of the 

 apothecia; but later observers have discovered that their 

 only safe rule of guidance is 



" In medio tutissimus ibis." 



By taking the characters of the thallus as a base, we are 

 compelled to group together Lichens having the most op- 

 posite fructification ; while by assuming those of the apo- 

 thecium we place side by side species possessed of the most 

 dissimilar vegetative systems : in either case the harmony of 

 nature is offended by the unnatural combination. It is xmly 

 by regarding together the vegetative and reproductive sys- 

 tems, — their minute or microscopic anatomy, as well as their 



