Fink: Classification of Lichens 
143 
cells become entirely emptied. In spite of this evidence of com- 
plete parasitism of the fungus, some botanists claim that the alga 
is benefited also.” We believe that this statement portrays fairly 
well the relation of the lichen to its algal host. 
Elenkin has accomplished some very illuminating work regard- 
ing the parasitism or the saprophytism of lichens. He found 
(48) hyphae of Lecidea atrobriinnea (DC.) Schaer. piercing into 
the algal cells in most instances after the cells were disorganized 
and empty, but rarely into uninjured cells. He observed a similar 
relation between Haematomma ventosum (L.) Stein, and its algal 
host and felt uncertain about the role of the distorted hyphae 
found within the algal cells. He thought that the hyphae brought 
about probably through an enzyme, the destruction of the cell con- 
tents and finally of the walls of the algae for nourishment. 
Whether the lichen hyphae penetrate into the algal cells or work 
from the outside of the cell wall, he regards .this method of 
nourishment endosaprophytism, since he thinks the role of the 
hyphae is to absorb dead rather than living matter. His second 
paper (49) enlarges on the first by treatment of a new series of 
lichens, but seems to add nothing otherwise. In a third paper 
(50) he states that his hypothesis is supported by the great abun- 
dance of dead algal cells in lichen thalli. He found that in thin 
sections stained carefully, the dead algae often exceed the liv- 
ing in numbers. He admit^that death may be due to parasitism 
of the lichen on the alga, or to lack of air and light. In favor 
of the enzyme and endosaprophytism hypothesis he thinks is the 
presence of dead algae in greatest proportion in the haustorial 
zone, in which most of the algae occur. Here the lichen hyphae 
form a compact layer about the algae, so that the enzyme could 
easily deform and destroy the cells, which would then assume 
irregular shapes, while their protoplasts would become pale and 
disappear. Similar destruction of algae continues in the cortex, 
until the last vestige of algal protoplasts and walls are consumed, 
he thinks the latter at least saprophytically. Some algal cells re- 
main rounded until after their protoplasts have disappeared. 
These are probably the ones that produce daughter cells vegeta- 
tively. Empty, dead algal cells surpass the living ones only in 
the haustorial zone of the thallus, while if reproduction ac- 
