Lichen-formtng Fungi. 49 



stance fungi were parasitic on algae at the expense and 

 ultimate destruction of the latter, and that the present 

 perfect mutualism between alga and fungus has been 

 acquired by degrees. Differences of degree are ob- 

 servable in the parasitism of fungi on phanerogams 

 at the present day, although no known examples of 

 true mutualism, between fungi and phanerogams are 

 known to exist. Numerous species of lichens are 

 parasitic on the evergreen coriaceous leaves of phane- 

 rogams. In the genera Goniocybe, Sphmctrina, 

 Calicium', &c., universally acknowledged by licheno- 

 logists as lichens, several species have no trace of 

 gonidia or algge, and in the terminology of lichenolo- 

 gists, the thallus or portion containing algge is then 

 said to be obsolete, but it is not difficult to realize that 

 certain species belonging to a given genus of fungi 

 have acquired the condition of mutualism with an 

 alga while others have not done so. The fungal con- 

 stituent of the great majority of lichens belongs to the 

 Ascomycetes, but recently two small groups of lichens 

 have been discovered where the fungus element 

 belongs to the Basidiomycetes and Gastromycetes 

 respectively. It is only fair to state that even at 

 the present day most of the leading liehenologists are 

 entirely opposed to the views stated above regarding^ 

 the nature of lichens, and consider that the whole 

 lichen, including what has been termed alga and 

 fungus respectively, can be produced from the spore 

 of a lichen, but it is important to bear in mind the 

 fact that no one has demonstrated this supposition, 

 and although much has been written by liehenologists 

 supporting the autonomy of lichens, not a particle 



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