THE LICHEN SYMBIOSIS 215 



protonemata of Mosses ^, the prothalHa of Pteridophyta, not to men- 

 tion the connection with larger algJB as tlie endoparasites of Fucoids ~. 

 Such phenomena at once introduce the difficulty of determining what 

 is really a sini])le Fungus-attack, and what is to be regarded as attaining 

 the dignity of a Consortium. The Fungi, again, follow the general 

 formula of known Ascomycete or Basidiomj^cete groups ; there is 

 nothing very exceptional about them in their more characteristic 

 reproductive processes ^ ; the hymenium is always normal ; as, for 

 example, in details of ascus-production, or protection, as also in 

 spore-discharge or septation, with few anomalies ; they show nothing 

 that is new beyond what may be ex:pected in quite ordinary liolo- 

 saprophytic Fungi *. But, once * synthesized,' to use the commonly 

 accepted expression, they apparently acquire a wholly new somatic 

 organization, giving them a morphology and habit all their own ; 

 and it is this latter relation that is to be expressed by the term 

 ' consortium ' and 'dual organization.' The botanists who first 

 demonstrated the algal nature of the ' gonidia,' being more concerned 

 with the story of the reproductive processes, or the actual establish- 

 ment of the synthesis, were less impressed by this remarkable conse 

 quence (De Bary, ISGo ; Schwendener, 1868 ; Stahl, 1877 ; Bonnier, 

 1889) ; and later writers (Reinke, 1895 ; Goebel, Organography, 

 Eng. Trans. 1900) first drew attention to it. The expression ' dual 

 organism,' of course, may be used quite as well for a Co7'flyce2)s 

 growing from a living caterpillar, or even for a tree-trunk with 

 abundant Polypori emerging from it, or, again, smothered in Mistletoe ; 

 but such combinations are clearly not intended to be included in the 

 conception of a * consortium ' — that is to say, the expression ' dual 

 organism ' is meaningless unless it is intended to cover a dual control ; 

 though it may be difficult to determine exactly where such dual 

 control may be localized, when two organisms are not in direct proto- 

 plasmic continuity, beyond each going its own way irrespective of 

 the other, so far as possible. Definite examples of dual organism are 

 presented in grafted trees, with fusion of conductive tissues ; but 

 this would not be regarded as a successful natural type of organism. 

 The most perfect expression is that of Plant-chimseras, with plasmic 

 fusion and growing point in common, with ready separation of the 

 two constituents (cf. Cytisus Adami and Solnnum tuhingense ; 

 Winkler, 1908 ; Berichte, p. 595). But even in these most inti- 



^ Cf. Bonnier, Ann. Sci. Nat'. Ser. 7, ix. p. 29 (1889), for the g-ermination of the 

 spores of Physcia on Vaucheria, with failure to produce symbiotic union, as ' no 

 false tissues.' 



2 Cotton, Brit. Myc. Soc. Trans, iii. p. 92 (1909), for 9 species of Pyrenomycetes 

 parasitic in marine Algae : Mycos'phierella of Pelvetia and Ascophyllum. 



^ The process of fertilization (sperniatogamy) involving a ' trichogyne ' is left 

 for further discussion. 



"* Much the same applies to the so-called Basidiomycete Lichens (cf. Cora, in 

 which there is very little special ' soma ' that can be called a consortium). Old 

 Polypori, growing on trees in this country, commonly become bright green on 

 the ui^per surface with encrusted Pleurococcus, and section shows that green algal 

 pockets may be 'intrusive' to a depth of 100 ju or more, as a ' gonidial ' zone, 

 without being regarded as forming a lichen consortium. It is evident that the 

 phenomenon may exist in all grades of ' intrusion ' and ' parasitism.' 



