REV. J. M. CE0MBIE ON THE ALGO-LICHEN HYPOTHESIS. 271 



that they possess no " involving " power whatever, as the Schwen- 

 denerians assume. The hyphse of Fungi, on the contrary, being 

 soft and flexible, readily involve and enclose foreign substances, 

 and indeed morphologically require the faculty of repeated con- 

 tortions, in order to form the cellulose nucleus of the receptacle 

 {cfr. Osw. Kihlman, Entwickel. der Ascomyceten, 1883). There 

 is evidently, therefore, no fungal mycelium in the lichen. 



Again, with respect to the gonidia, notwithstanding their 

 general resemblance to certain of the lower algals, it by no means 

 follows that similarity is identity, — the two things being logically 

 very different. The circumstance of the lichen-gonidia being 

 subsimilar to such Algae in form and structure only shows that 

 there is a certain "parallelism" between them, and does not 

 militate against both being regarded as belonging to distinct 

 classes of plants*. Indeed the chlorophvll, or phycochrom, in 

 Lichens originates in the same way as in the cellules of other 

 classes of plants (Phanerogams and Cryptogams) in which it 

 occurs ; the only difference being that the gonidia are often seen 

 as discrete cellules, although many forms variously composed are 

 also not uncommon. Moreover, many genera and species for- 

 merly supposed to be algals, and regarded by Schwendenerians as 

 furnishing gonidia to lichens, have of recent years, in consequence 

 of the discovery of their fructification, been proved to belong to 

 lichens. Thus Sirosiplwn, Hormosiphon, Scytonema, S/igonema, 

 Cora, Dichonema, Chroolepus or Trentepohlia, Nostoc, and Oloeo- 

 capsa (at least in part), Gongrosira, and probably Phyllactidium, 

 have now to be removed from the class of the Alga?, and conse- 

 quently can no longer be pressed into the service of the Algo- 

 lichen hypothesis f. In other respects the various forms of 

 lichen-gonidia are so well-marked as to admit of a distinct classi- 

 fication and nomenclature of their own. These have been elabo- 

 rately expounded by Ny lander, with diagnoses of the different 



* Such parallelism was long ago well pointed out by Thwaites in a paper 

 " On the Gonidia of Lichens " (Ann. & Mag. Nat. Hist. 2 ser. vol. iii. 1849). 

 He rightly saw in the similarity of the gonidia to the Algffi, not identify, but 

 only "a typical character of essential structure binding together numerous 

 species of various forms, and enabling us to distinguish at once in other species 

 resemblances of analogy from those of affinity." 



t Nor does the evolution of zoospores in free gonidia (». e. in unstratified 

 thalli), as in Chroolepus, at all identify such gonidia with algals, since in this 

 there would again be only a similarity, and nothing contrary to the nature of 

 lichens. 



