Fink; Classification of Lichens 
145 
shriveled and irregular in form, gradually disappearing and re- 
placed by the larger hyphae. During this process, the algal cells 
become pale, and many empty cell walls also remain. In an early 
stage of parasitism of a hypha on an algal cell, when the hypha 
has just become appressed and enlarged, the algal cell is irritated 
and divides rapidly, forming new cells, which are free for a 
time. These are later attacked by the lichen hyphae. Danilov 
makes nothing of Elenkin’s theory of endosaprophytism, but 
thinks rather that the lichen is purely parasitic on the alga. Of 
course the relation is wholly antagonistic in either case. 
Treboux (134) in a more recent research thinks it hardly sup- 
posable that the lichen receives any considerable portion of its 
organic material from the algal host, or that the alga depends upon 
the lichen to any appreciable extent, even for carrying water, 
mineral salts or organic food from the substratum. He thinks it 
much more probable that the alga obtains both moisture and 
nourishment mainly from the air. He mentions Beijerinck’s 
work on algae supposed to obtain carbon from peptone compounds 
and states that Cystococciis hiimicola belongs here and is the 
host of many lichens. He thinks there are really no peptone algae 
but rather that most algae can get their carbon from peptone 
compounds under certain conditions, and from the air under other 
conditions. So an alga may have one source of carbon when 
serving as the host for a lichen and a very different one when free, 
and the lichen may lay hold of free Cystococcus hiimicola, which 
will at once change its method of nutrition. If this be true, it is 
no longer necessary that we should think the method of nutrition 
changed through long living with a lichen. After comparing the 
Cystococcus forming lichen hosts with other algae, he concludes 
that it is an independent species, distinct from both Chlorococcum 
and Pleurococcus. Neither the free Cystococcus nor specimens 
recently isolated from lichen thalli is much given to zoospore for- 
mation. The free-living Cystococcus hiimicola shows the same 
characters as the lichen host, except for modifications caused by 
parasitism, and quickly assumes the usual form and method of 
nutrition when freed. Both the free algae and those recently lib- 
erated from lichen thalli readily pass into the hostal relation with 
lichens in cultures. The alga grows and reproduces much more 
