194 Transactions British Mycological Soctety. 
of importance occurred in the gonidia of Peltigera malacea, and 
that he thinks may indicate some specific difference or only 
some particular physiological race. 
Waren (1920), a pupil of Elfving, has chiefly been occupied 
with bright-green gonidia which he cultivated from twenty-one 
different species of lichens. He tested them on different nitro- 
genous media and found that they grew most freely on amino- 
acids. He classifies the gonidia of most of our common lichens 
under the genus Cystococcus which he divides into two sections, 
Eucystococcus, in which there is vegetative division (Protococcus), 
and Eleuterococcus, the species of which apparently form 
autospores in the cultures. The gonidia from the different 
species show differences of form and colour in the culture 
colonies which leads him to think that each lichen species has 
its own particular gonidium. Bioret (1921) however thinks that 
in organisms so polymorphic as green algae it is impossible to 
determine aberrations as specific or even racial. Waren found 
that the gonidia in Xanthoria parietina from Finland differed 
from those of the species collected in Holland. 
Waren’s views on the gonidium do not accord with those of 
Paulson (1921) published in last year’s Transactions of this 
Society. The latter dealt with the living thallus and found in 
a very large number of lichens the same type of sporulating 
gonidium present which he refers to Chlorella sp. 
SYMBIOSIS OR PARASITISM. 
The nature of the association between the two organisms in 
the lichen thallus is still under discussion. Paulson (1921) main- 
tains the necessity of regarding both organisms living in a 
healthy condition as symbiosis, as neither succumbs to the other. 
The alga is not parasitized; it sporulates abundantly at certain 
seasons and any dead members are due to the natural process of 
decay. Eva Mameli (1920, 4) has arrived at the same conclusion 
as a result of her study of the thallus. She found occasional dead 
algae but these were chiefly in the deeper layers where light is 
scanty, and in purely algal colonies such dead members are 
equally present. The possibility of the fungal haustoria piercing 
the algal cell is not ruled out, but it happens so rarely, that it 
is impossible to regard parasitism as a necessary condition. 
Bachmann (1922) in further work on calcareous endolithic lichens 
finds in nearly all of those examined that the gonidia, Seytonema 
or Trentepohlia, live side by side with the hyphae. The Scyto- 
nema filaments (in Petractis clawsa) are surrounded by small- 
célled hyphae which are in contact but never penetrate. Certain 
free filaments travel deeply into the rock, and there die off more 
quickly than those closely associated with hyphae. 
