Fink: Classification of Lichens 
127 
Bonnier (31) seems to have been first to produce mature, 
fruited lichens in cultures. He raised Xanthoria parietina (L.) 
Th. Fr. with an alga which he called Protococcus and succeeded 
in getting a thallus that bore an apothecium. With the same alga, 
he obtained fully developed thalli of Physcia stellaris (L.) Nyl. 
and Parmelia acetabulum (Neck.) Dub., but he got no apothecia 
in these. He sowed Rinodina sophodes (Ach.) Koerb. with 
Pleurococcus and got well-developed thalli with apothecia. 
Lecanora ferruginea (Huds.) Nyl., Lecanora subfusca (L.) Ach., 
Lecanora coilocarpa (Ach.) Nyl. and Lecanora caesiorufa (Ach.) 
Nyl. grew to maturity with the same alga in two to four years, 
but none of these produced fruits. Unless he was mistaken in 
his alga, the algal host was not only wild but also unusiial ; but he 
might easily have mistaken Chlorococcum for Pleurococcus. 
Spores of Opegrapha vulga'ta Ach. sown with Trentepohlia pro- 
duced good thalli as did also V err uc aria muralis Ach., in less than 
a year. He got Lecanora atrorufa Ach. spores to germinate on 
Trentepohlia and Lecanora subfusca (L.) Ach. spores on Vau- 
cheria sessilis. The former showed haustoria and a poor devel- 
opment of plectenchyma, but the latter produced the plectenchyma 
only. All of these were cultures with wild algae, and prove that 
these algae are quickly modified, when parasitized, into the forms 
usually found in lichens. 
Tobler (130) cultivated Xanthoria parietina (L.) Th. Fr. with 
and without an alga. He found that when the lichen grew alone, 
the yellow parietin was not developed ; and treatment with acids 
and alkalis did not produce the characteristic coloration. In cul- 
tures of the same age with the alga, he got the yellow parietin 
and the characteristic chemical reactions. Zopf (148) has sum- 
marized these peculiar chemical reactions and the colors produced 
in lichens, and Tobler’s results indicate that all of these chemical 
reactions and colorations are due to the peculiar relation of the 
lichen to the algal host, the former plant not being able to produce 
them alone. So the lichen differs from other fungi in the pro- 
duction of peculiar substances when it grows with the host. 
The greatest advantage of parasitism on the algal host has been 
supposed to be that the lichen received carbon, which the alga 
