262 BEY. J. M. CBOMBIE ON THE AL GO -LICHEN HYPOTHESIS. 



a " lichen," inasmuch as this also is partly furnished by means 

 of the substratum. 



Passing over two other and subsequent papers of Schwendener, 

 viz. " Erorterungen zur Gonidienfrage " (in ' Flora,' 1872) and 

 " Die Flechten als Parasiten der Algen " (in Verhandl. der 

 Naturf. Gesellschaft in Basel, 1873), in which, after replying to 

 several objections that had been adduced by Krempelhuber * and 

 Th. M. Fries, he maintains and further illustrates the hypothesis, 

 though without adducing any absolutely new arguments, we now 

 come to notice the contributions made to the theory by Dr. E. 

 Pornet, in some respects the ablest and most plausible of its 

 advocates. In a memoir entitled " Eecherches sur les Gonidies 

 des Lichens" (in Ann. des Sci. Nat. 5 e ser. t. xvii., 1873), he 

 accepts in its full extent Schwendener's theory as the only one 

 capable of explaining satisfactorily many obscure phenomena 

 in the morphology and physiology of Lichens. After pointing 

 out that Schwendener did not sufficiently show that the relations 

 between the hyphae and the gonidia were such as necessarily to 

 involve the idea of parasitism, and arguing that the great simi- 

 larity between the gonidia of Lichens and certain Algal types was 

 not an accidental circumstance, he passes in review an extensive 

 series of Lichens belonging to numerous different genera. Adopt- 

 ing the two Algal groups of Schwendener, already referred to, he 

 examines first the Chlorophyllacea?, viz. Trentepohlia, Mart., 

 Phyllactidium, Kiitz., Protococcus, Ag. Of these he traces the 

 resemblance between Trentepohlia and lichen-gonidia in thirteen 

 genera, viz. : — (1) Boccella, as already shown by Schwendener ; 

 (2) Zecanora, in many species ; (3) Birina repanda, Fr. ; (4) Cceno- 

 gonium LinMi, Ehrh., and C. confervoides, Nyl. ; (5) Bgssocaulon 

 nive-um, Mont. ; (6) Lecidea lutea (Dicks.), and L. microsperma, 

 Nyl. ; (7) Grapliis elegans, Aeh. ; G. contexta, Pers., and G. 

 heterospora, Nyl. ; (8) Opegrapha varia, Pers., and 0. lierbartm, 

 Mont. ; (9) Stigmatidium crassum, Dub.; (10) ArtJionia cinnaba- 

 rina, AVallr. ; (11) Melaspilea arthonioides (Fee) ; (12) Chiodec- 

 ton tngrtlcola, Fee, and C. nigrocinctum, Mont. ; (13) Verrucaria 

 nitida, Sc'nrad., in which, as well as in several Graphidei, it had 

 formerly been recognized by De Bary. The genus Phyllacti- 

 dium he regards as furnishing the gonidia to Opegrapha jilicina, 

 Mont. ; while a species of Protococcus, viz. P. viridis, is similar to 



* In ' Geschichte und Litteratur der Liehenologie,' iii. Bd. (1872). 



