108 
Mycologia 
than those in which the lichen ramifies throughout the algal 
colony. More difficulty will probably appear in the crustose than 
in the foliose and the fruticose species. In the descriptions of 
many genera and species of lichens, the only changes needed are 
to remove whatever is said of the algae from the descriptions and 
to modify in some manner the statements regarding the so-called 
algal layer and the soredia. In thalli which contain the algae in 
a definite stratum, the algal layer may well be called the haustor- 
ial layer. This has the advantage of excluding from the state- 
ment an organism which does not belong to the lichen. The sor- 
edium should be regarded as a tangled mass of lichen hyphae and 
haustoria. 
Perhaps few botanists had thought that so great changes in the 
treatment of lichens and consequent difficulties in using the liter- 
ature of lichenology were involved, unless these plants were dis- 
tributed to the exclusion of the group Lichenes. The trouble 
really appears when we consider lichens properly as fungi, 
whether we distribute them or not ; though the less fundamental 
matter of distribution does offer even more intricate problems. 
Treating together as colonies the lichens and the algae which 
occur with them and continuing to describe and classify these 
colonies is the only way to avoid the enormous amount of labor 
involved in revision. This is, of course, wholly illogical, and the 
only consistent course is to break with past methods and treat 
lichens rightly, regardless of the difficulties which present them- 
selves. 
The Biological Relations of Certain Lower Lichens 
By considering carefully some lower lichens and some plants 
that may not be lichens, we will be able to gain information re- 
garding the relation of lichens to their algal hosts and to other 
fungi. Those who hold to some form of dual hypothesis insist 
that these lower and doubtful lichens are atypical and should not 
be considered; but the largest groups of lichens are among the 
lowest forms. Hence, the lowest lichens are interesting and in- 
structive in consideration of problems relating to the nature and 
the disposition of these plants in general. Their study throws 
light upon phases of the problem which can scarcely be under- 
