444 



II. 



The Systematic Position of Lichens.* 

 This paper is a critical review of lichenology since the time of 

 Schwendener's epoch-making investigations.! The author credits 

 De Bary with first having indicated the dual nature of Hchens by 

 demonstrating that species of Nostoc and CJiroococcus may be con- 

 verted into gelatinous lichens upon becoming penetrated with the 

 hyphae of certain parasitic Ascomycetes. It must be remembered 

 that as late as 1863 Schwendener still believed that the gonidia 

 (algae) were developed upon lateral and terminal branches of the 

 hyphae.J De Bary made his discovery in 1865. In l868§ 

 Schwendener accepted this view and added that all lichens were 

 the result of the union of an alga with some fungus. As the re- 

 sult of his investigations Schwendener concludes that lichens 

 should no longer be considered as a distinct class, but as fungi 

 parasitic upon algae (gonidia). He states : " In development the 

 vegetative organs and the organs of reproduction of lichens are in 

 all respects similar to those of Ascoiuycetes." Reinke has always 

 agreed with Schwendener in the belief that the gonidia of lichens 

 were true algae and the hyphae true fungi. Their opinions differed, 

 however, as to the relationship of the two organisms. Reinke was 

 not at all willing to look upon it as a form of ordinary parasitism. 

 During the summer of 1872, in verbal communication with Griese- 

 bach, Reinke pointed out that the relationship indicated a mu- 

 tual benefit. While the alga supplied the fungus with assimilated 

 food-substances, the latter supplied the alga with water, nitrogen, 

 phosphorus, sulphur and mineral salts. The relation of the fungus 

 and alga in the lichen was comparable to the relation of the root 

 and the leaves of a tree. In order to distinguish this form of re- 

 lationship (symbiosis) from parasitism (antagonistic symbiosis) it 

 was necessary to introduce a new term. Reinke and Grisebach 



* Reinke, J. Die Stellung der Flechten im Pflanzensystem. Pringsheim's Jahr- 

 biicher, 26: 524-542. 1894. 



f Schwendener, S. Die Algentypen der Flechten-gonidien. Basel, 1869. 



:j: Schwendener, S. Nageli's Beitrage zur Wissenschaftlichen Botanik, 3: 133- 

 136. 1863. 



I Schwendener, S. Nageli's Beitrage zur Wissenschaftlichen Botanik, 4: 195- 



202. 1868. 



