Fink: Classification of Lichens 
141 
its algal host. Warming (140) uses Schwendener’s term, “ helo- 
tism,” to express this relation. He believes that the alga grows 
and reproduces rapidly in the lichen through hypertrophy, a 
pathologic condition, and that it is hindered from zoospore forma- 
tion. Lindau (81) thinks that the lichen is parasitic on the alga, 
and that the many dead algal host cells result from lack of air 
and from the absorption of food by the lichen hyphae. Schnei- 
der’s most extended statement ( 1 1 1 ) is to the effect that “ in indi- 
vidualism is reached the acme of mutualistic association.” He 
then proceeds to tell us that individualism requires that one of the 
symbionts shall be absolutely dependent upon the other, a con- 
dition which he thinks is found in lichens. He admits that the 
algal host may live without the lichen parasite, but thinks that 
since the lichen can not get on alone, it and the algal host together 
form a new physiological and morphological individual. He 
thinks that at some future time neither symbiont will be able to 
live alone, and that individualism will then have reached its acme. 
What fungus can get on well without its host? And what evi- 
dence have we, while the alga continues to thrive better alone than 
when parasitized, and while lichens are commonly found growing 
near the algae which they parasitize from time to time, that the 
algal host will one day be unable to live without the fungal 
parasite ? 
It is time to be done with these unproved and hopeless hypoth- 
eses of mutualism, consortism and individualism and turn to 
something more promising. In spite of all these hypotheses, the 
lichen is still parasitic, or more likely partly parasitic and partly 
saprophytic, on the alga. Those algal cells which are not invested 
or penetrated by lichen hyphae are usually of normal size and 
form and are darker green than those in the same thalli that are 
invested or penetrated by the hyphae. The lichen haustoria surely 
take from the algae foods which these algae have elaborated for 
their own nourishment. This must injure the algal host cells 
seriously and often kill them, for many of the algal cells in lichens 
are dead and devoid of protoplasm. The bright green cells which 
one finds in lichen thalli are those algal cells which have recently 
resulted from division. They are not yet parasitized, or have 
been parasitized but a short time. The results are the same 
