THE FUNGI 97 
THE LICHENS 
In connection with the true Fungi there must be con- 
sidered the Lichens. While there is no doubt that these 
are sufficiently distinct to form a separate class, never- 
theless their obvious relationship to other fungi, mostly 
Ascomycetes, forbids the establishment of a subkingdom 
coérdinate with Alge and Fungi. 
These curious organisms exhibit a remarkable type 
of parasitism, or perhaps better, symbiosis, where two 
plants, an alga and a fungus, are so intimately associ- 
ated as practically to form a single plant. An exami- 
nation of the thallus of a lichen shows it to be made 
up of densely woven and more or less coherent hyphae, 
among which are found numerous green cells. The 
latter are usually aggregated near the outside of the 
thallus, and a careful examination shows them to be 
certain low alge, which can be readily identified as 
species often growing quite apart from the lichen. 
If these alge are isolated, and given proper conditions 
for growth, they flourish perfectly, showing that they 
are not, in any true sense of the word, really dependent 
upon the lichen for their existence. While in some 
respects the hyphe of most lichens differ somewhat 
from those of other fungi, still the general structure is 
very similar, and the fructification corresponds exactly 
with that of typical fungi, especially the Ascomycetes, 
to which most lichens are undoubtedly related. A few, 
however, are Basidiomycetes. 
It was supposed by the earlier students of the lichens 
that the green cells were direct outgrowths of the color- 
less hyphz, but the more careful investigations of later 
H 
