214- THE JOURNAL OF BOTAXY 



may be investigated and catalogued by special monographers ^ as 

 a wholly new and unique development in subaerial vegetation ^. One 

 is thus encouraged to regard a Lichen as a pleasing triumph of social- 

 istic biology, the expression ' dual organism ' being meaningless, 

 unless it also implies a divided control, and that the Lichen, so to 

 speak, has not a soul to call its own. On the other hand, it is often 

 difficult to convince the wholly unbiassed student that there is any- 

 thing in the phenomena beyond the pure holoparasitism of a special 

 set of Fungus phyla, admittedly polyphyletic as are other phenomena 

 of jmrasitism, and that the ' symbiosis ' is wholly imaginary or 

 woefully exaggerated. The general facts of the story may be there- 

 fore examined in further detail ; since whatever be the present state 

 of the relation of the component organisms, there can be no question 

 that such a biological phenomenon must have had a remarkable 

 origin ; and all the greater interest will centre in the discussion of the 

 conditions which may have induced such a state of affairs. 



The word s3anbiosis, borrowed from zoological usage is admittedly 

 a perfectly meaningless expression, in that any strict definition as to 

 what is intended, from the\'dgimi^i co??i mensalism is pure JioIo]yarasifis)fi, 

 has to be read into it arbitrarily ; and in such case, as often happens, 

 it may be employed as a dangerous half-truth to obscure the really 

 interesting facts of the more fundamental nature of the association ^. 

 In the widest sense of ' mutual benefit ' to both parties concerned, 

 however small the advantage may be to one of them, there can be no 

 objection to its use ; but this is a proposition very different from 

 * the evolution of a dual organism.' It is the 'consortium' which 

 requires fuller justification : what exactly may be intended in the 

 connotation of such a term, and how it is biologically expressed 

 in novel form, as something quite distinct in the realm of modern 

 vegetation. The general facts are sufficiently clear and accepted. 

 The ' gonidia ' of a Lichen are admittedly simple algal protoplasts, of 

 typically discrete organization, averaging 10-12 fj. diam., in all more 

 successful Lichens, and they belong to groups of lowest grade Alga? ; 

 whether more 'primitive' (Cyanophycea?), or decadent and aflagel- 

 late (as Protococcoidea?) ; less frequently Ulotrichales of fresh-water 

 rather than marine habitat {Trfnffj)o}iIm=ChroolfjJus) ^ ; in which 

 somatic organization is reduced to the limit of simplicity ^, and 

 reproductive organization is wholly wanting or omitted. Cases in- 

 volving more distinctly filamentous algal growth, as in coenocytic 

 Cladojiliora and Vauclieria, are unconvincing, since the symbiosis 

 does not attain either a reproductive stage or a tissue-system in the 

 soma; and such cases grade into the condition of simple parasitic 

 attachment noted in the association of Fungus hyphse with the 



^ A. L. Smith, Monograph of the British Lichens (191S). Crombie, Monograph 

 of British Lichens (1894). Krempelhuber, Lichenologie {Geschichte und Lit- 

 teratur) (1867). 



2 Reinke, Jalirbiicher Wiss. Bot. Prings. pp. 39-70 (1895). 



•^ Lumiere, Le Mythe de Symhiotes (1919). Bernard, Ann. Sci. Nat. 9 Ser. ix. 

 1, L'Evolution dans la Symbiose (1904). 



■* A. L. Smith, op. cit. p. x. West, Algx, i. p. 141 (1916). 



■^ West, 7oc. oi7. Aeton, Ann. Eot. xxiii. p. 579(1909): '' Botrydina vulgaris, 

 a • primitive Lichen.' " 



