34 On the Dissociation of a Lichen. [Sess. 



that some nourishment was obtained from the algal cells. 

 Treub was terribly troubled with mould growing in his cul- 

 tures, as was naturally to be expected from the method he 

 adopted, and although he made a very great number of cul- 

 tures, and took a vast amount of trouble, none of his cultures 

 survived more than a few weeks ; and upon the whole his 

 opponents, the lichenologists, were right in maintaining that 

 his experiments did not go far to solve the problem. 



The next great observer who made an elaborate contribution 

 to the subject was Bornet ('Ann. Sc. Nat. Bot.,' 1873). He 

 lays emphasis on the fact that the relation between green cells 

 and the colourless filaments was hardly known, and it was 

 very important to observe that the green cells did not arise 

 out of the colourless hypha?. In other words, he showed that 

 there was no genetic relation between the one and the other. 

 Bornet studied sixty genera of lichens, and described the algae 

 which belonged to them. The kinds of algte to which the 

 gonidia seemed to belong were far fewer than sixty, one species 

 of alga serving as the guest of a number of lichens. Although 

 Bornet's paper is admirable in the highest degree, it throws 

 hardly more light than Treub's did on the real solution of the 

 problem. 



The last contribution to this phase of the question which I 

 shall mention is one by Bonnier ('Ann. Sc. Nat. Bot.,' 1889). 

 The author used Pasteur flasks and pieces of hard rock steril- 

 ised at 115° C, and maintained that he succeeded in pro- 

 ducing lichens from lichen spores and real alga?, — not from 

 gonidia, as the other investigators had done. He used Pro- 

 tococcus and other unicellular algse. 



Now we turn to the other aspect of the question — the dis- 

 sociation of lichens. Two excellent observers, Faminzin and 

 Baranietsky (' Botanische Zeitung,' 1887), took thin sections 

 of lichens, as well as pieces of the thallus, and cultivated them 

 for some weeks on fir bark in a moist atmosphere, allowing 

 water to drop upon the bark from a siphon. The structure 

 of the lichen was softened, and here and there completely 

 destroyed. The gonidia, however, remained quite sound, and 

 after two or three months zoospores were observed. No 

 remark is made in the account the authors give of their 

 experiments as to sterilising the water which dropped from 



