258 



Mycologia 



me that the term lichen rightly understood is more an ecological 

 expression than it is morphological or taxonomic. A fungus and 

 an alga form a peculiar type of association, and we call that asso- 

 ciation a lichen. Originally the term may have had some 

 morphological foundation, but it has certainly now become so ex- 

 tended that its only significance is that of a special type of asso- 

 ciation. It is true that the association is often of an exceedingly 

 intimate character involving morphological changes of a funda- 

 mental nature, but this is true of associations everywhere. There 

 appears to me no more reason to treat the lichens as a distinct 

 taxonomic group than to separate out the plants of the salt marsh 

 because they are Halophytes. The Lichens represent a highly 

 specialized ecological group, but still ecological and not morpho- 

 logical and by no means taxonomic. According to the biological 

 conceptions of to-day taxonomy is the attempt to express in 

 diagrammatic form the phylogenetic relationships of the organic 

 world. To constitute the Lichens a distinct taxonomic group 

 would be a violation of our present conceptions, for there is no 

 reason to believe that the lichens as such have sprung from a 

 common ancestral type. The taxonomy of these plants ought 

 to be built upon the fungal rather than the algal phylogeny. For 

 the algal portion, I believe in all cases, can and does maintain an 

 independent existence, and as autonomous organisms have re- 

 ceived their proper taxonomic treatment. Moreover the algal 

 portion undergoes little morphological modification by reason of 

 the lichen association, and hence their separate treatment in this 

 way will not introduce confusion. The fungal portion on the 

 other hand has in most instances undergone profound modifica- 

 tion by reason of the association, and many of them are unable 

 to maintain an existence separate from the alga. For this reason 

 the fungus is always determinative of the association and the 

 taxonomic classification must express the fungal relationship. In 

 some instances there is undoubtedly a true lichen phylogeny, that 

 is, forms have arisen by modification of a primitive lichen type. 

 These would constitute genera and perhaps families all having 

 the lichen habit, but this would not affect the general principle 

 that ought to control the classification of these plants. I am 

 aware that the argument offered applies in considerable degree 



