M. C. COOKE ON THE DUAL-LICHEN HYPOTHESIS. 171 



sought out, or indeed caught hold of, and compelled into its service. 

 It surrounds them, as a spider its prey, with a fibrous net of narrow 

 meshes, which is gradually converted into an impenetrable covering ; 

 but whilst the spider sucks its prey and leaves it dead, the fungus 

 incites the algae found in its net to more rapid activity — nay, to more 

 vigorous increase.""* 



In the volume " Fungi " in the International Scientific series, 

 from page 10 to page 16, the theory in question is thus ex- 

 plained : — 



" The two great points sought to be established are these, that 

 what we call Lichens are compound organisms, not simple, inde- 

 pendent vegetable entities ; and that this compound organism 

 consists of unicellular algae, with a fungus parasitic upon them. 

 The coloured gonidia which are found in the substance or thallus 

 of lichens, are the supposed Algae, and the cellular structure which 

 surrounds, encloses, and imprisons the gonidia, is the parasitic 

 fungus, which is parasitic on something infinitely smaller than itself, 

 and which is entirely and absolutely isolated from all external in- 

 fluences, "f 



In plain words, the gonidia are algae, and all the rest of the plant 

 is Fungus. At first sight it would appear that the whole con- 

 troversy centered itself upon the definition of two words. A certain 

 plant, with a peculiar organisation, has been hitherto by general 

 consent represented by the term Lichen, whereas some modern 

 writers contend that it should be called a Fungus, differing only 

 from other Fungi in its power of enclosing certain unicellular algae 

 within its substance. Shall these organisms still retain the name 

 of Lichens, or shall they be called modified Fungi ? This is really 

 one aspect which the hypothesis assumes, that of the value of two 

 words. The theorists, on their part, maintain that it is something 

 more than a mere definition of terms which is required, but they 

 claim to have it accepted that Lichens (as they are called) are iden- 

 tical with Fungi (as commonly understood) , but with the addition of 

 certain extraneous bodies called "gonidia," which are truly micros- 

 copic Algae. 



Some general objections to the hypothesis will afford evidence that 

 there is still a broad space between the theorists and some of their 

 opponents. 



* Schwendener, " Die Algentypen der Flechtengonidien," p. 3, 1869. 

 t " Fungi, their nature, use," &c., pp. 11-12, 1875. 



