34 GUIDE TO THE STUDY OF LICHENS. 



descending series with those most nearly resembling 

 algae. From these considerations, it is evident that 

 the attempt to classify them either as fungi or algae 

 will lead to confusion. In agreement with Reinke, 

 Darbishire and others, we have decided to treat lichens 

 as a distinct class. The reasons for so doing will be 

 given later. 



In conclusion, we will briefly describe the algae 

 which enter into the formation of lichens. The figures 

 of Plate I represent the algae surrounded by the 

 hyphal network of the fungal symbiont. The fungal 

 types cannot be represented, for the simple reason 

 that they are not known ; the knowledge that they are 

 derived from some groups of the sac-fungi must suffice 

 for the present. The general belief is that the fungi 

 which originally entered into the formation of lichens 

 no longer exist. There are, however, fungi now liv- 

 ing which resemble the fungal symbionts of certain 

 lichens ; for example, the representatives of the fungal 

 genus Hysterium closely resemble the fungal symbiont 

 of the lichen-genus Ghraphis. 



I. Chlorophyce^. — The algae belonging to 

 this group are distinctly bright-green. The follow- 

 ing are the species which enter into the formation of 

 lichens, given in the order of the frequency of occur- 

 rence. 



1. Cystococcus humicola. This is a unicellular alga 

 occurring in far the greater number of lichens. The 

 cells are spherical. (Fig. 1.) 



2. Chroolepus umhrina. This alga forms short 



