444 
EE 
Tue 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 lichens by 
demonstrating that species of NMostoc and Chroococcus 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.t De Bary made his discovery in 1865. In 1868§ 
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 10 
all respects similar to those of Ascomycetes.’ 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 
gma 
* Reinke, J. Die Stellung der Flechten im Pflanzensystem. Pringsheim’s Jaht- 
biicher, 26: 524-542. 1894. 
+Schwendener, S. Die Algentypen der Flechten-gonidien. “Basel, 1869. 
Schwendener, S, Nageli’s Beitrige zur Wissenschaftlichen Botanik, 3: 133- 
136. 1863. 
§ Schwendener, S. Nageli’s Beitrage zur Wissenschaftlichen Botanik, 4: 195-~ . 
202, 1868, | 2 
