CHAPTER VII. PHENOMENA OF VEGETATION. LICHENS. 419 



young plant grown from the spore must meet at the same time with the Alga and with 

 suitable nutriment of other kinds that the experiments became decisive. Reess produced 

 Collema from its component parts with the thallus fully formed, but time was not allowed 

 for the development of the sporocarp. Then Stahl by judicious selection of the 

 objects to be experimented on effected the synthesis of three species of Lichens ; he 

 gave a complete demonstration of the entrance of the Alga into the composite Lichen, 

 the changes which it undergoes there and its possible ultimate liberation, and he suc- 

 ceeded especially in proving that the same Pleurococcus may appear as a constituent of 

 more than one species of Lichen. 



These results satisfied all demands and the Lichen-question was settled once for all 

 against the old traditional view. 



The discovery by Mattirolo that the thallus of Lichens may also be composed 

 of Hymenomycetous Fungi was a welcome confirmation and illustration of the new 

 view. 



There have in fact never been any real difficulties in the way of accepting 

 Schwendener's theory ; the only obstacle to be encountered was the tradition which 

 had been cherished for some centuries. It must be allowed that it is perhaps difficult 

 to realise, how when Lichens are growing socially in large numbers each one of them 

 is formed by synthesis of spore and free Alga. But in most cases it is not necessary 

 to suppose that this is the case ; the primary synthesis may take place only seldom ; the 

 large number of soredia produced will account for the most copious propagation of 

 the species which can be imagined. On the other hand Stahl's observations on the 

 hymenial Algae show that there are adaptations which almost ensure the synthesis 

 every time that spores germinate. Considering the great variety of forms in the Lichens 

 it is possible that many special adaptations may yet be discovered in the course of 

 time. Frank's work cited above supplies evidence in support of this view. It is more- 

 over quite conceivable that there are species of Algae which have become so adapted 

 to lichenism, that they can no longer attain their full development outside the Lichen- 

 combination, perhaps not even vegetate independently any longer 1 ; examples of the kind 

 are not at present known, but the possibility of their occurrence should be borne 

 in mind. 



Our historical sketch would not be complete without a record of the fact that since 

 the year i878 2 Dr. Arthur Minks has attempted to rescue the old tradition by the dis- 

 covery of a new organ termed a microgonidium which takes part in the formation of a 

 Lichen-thallus of quite different structure from anything described above. More than 

 this short notice cannot be expected from the author of a serious botanical work. 



LITERATURE OF THE LICHEN-THALLUS. 



'Geschichte und Litteratur der Lichenologie von den altesten Zeiten bis zum Schlusse 

 desjahres 1870,' by A. von Krempelhuber, a very remarkable work, gives in three volumes 

 containing altogether more than 1650 large octavo pages an account of the subject 

 indicated by the title-page, and a very careful notice of all the works connected with it. 

 The Regensburg ' Flora ' is a rich repertory of Lichenology since 1855. The reader is 

 referred once for all to these two publications for all literary and historical details. 



It is unnecessary to say anything more in this place about the various publications on 

 the sporocarps of Lichens and matters connected with them ; a sufficient account has 

 already been given of them in Chapters III and V. It remains only to name the 

 authorities from which our account of the Lichens has been derived, so far as they have 



1 See Frank, in Cohn's Beitr. z. Biol. d. Pfl. II. 



a Flora, 1878, p. 209. Also A. Minks, das Microgonidium, ein Beitr. z. Kenntn. d. wahren 

 Natur d. Flechten, 8. Basel, 1879. See also Just's Jahresber. 1876 and succeeding years. 



E 6 2 



