116 
Mycologia 
hyphae closely applied to all of the Trent epohlia filaments exam- 
ined, forming a delicate, reticulated, spirally wound network of 
hyphal tissue, entwining the filaments from the base to the apex 
and extending a short distance beyond. This fungus is probably 
a primitive and imperfect lichen, the fruit of which is unknown. 
Of course, it is possible that the fungus bears no nutritional rela- 
tion to the alga, but merely uses it as a support, on which to climb. 
If so, the fungus is not a lichen ; but this supposition is improbable. 
One sometimes finds Sirosiphon filaments attacked by other 
fungal hyphae than those of Ephebe. These hyphae are usually 
external, while those of Ephebe ramify through tlie algal fila- 
ments. These superficial hyphae bear somewhat the same rela- 
tion to Sirosiphon as do those found by Schneider to Trente- 
pohlia aurea, and they may represent some unknown lichen or 
lichens. The findings of Archer, given above, may well be re- 
called here. 
Many botanists have not known that the transitional forms 
connecting lichens with other fungi are numerous ; but among 
the Graphidaceae, the Arthoniaceae, other families of lower 
lichens and the fungi parasitic on lichens are hundreds and 
probably thousands of species whose biological position can only 
be known by careful research. Besides these, there are doubtless 
many more accidental associations of fungi and algae yet to be 
discovered. In view of these facts, the bridges connecting lichens 
with other fungi seem to be very numerous. 
Whether a given fungus is a lichen is of little, if any, biological 
importance, and is certainly of no taxonomic importance for those 
who believe that lichens should be distributed to the exclusion of 
the group Lichenes. But the biological relationship between fungus 
and alga is an important one, and the fungi which are partners in 
it will continue to be known as lichens. Hence, from a biolog- 
ical point of view, it is important to reach some conclusion touch- 
ing what constitutes a lichen. However, the main object of this 
discussion is to bring to light some of the very close but little 
known relationships of plants on the border line between lichens 
and other fungi. One may regard these as lichens or not. The 
relationship remains the same in either case, and research must 
discover many more such relationships before our knowledge of 
