100 EVOLUTION OF PLANTS 
the groups now exist, the three classes, Ascomycetes, 
AEcidiomycetes, and Basidiomycetes, have very little 
in common, although it is probable that the two latter 
have had a common origin. 
The Lichens must be supposed to have had a multiple 
origin, like the Phycomycetes. The majority have been 
derived from different groups of ascomycetous fungi, 
but some of them are allied to the Basidiomycetes. 
We may then consider the Fungi as an aberrant 
group of plants, probably — but not certainly — derived _ 
from originally green ancestors, but which have di- 
verged so widely from the parent stock that they have 
lost nearly all of their original characteristics. 
