Fink: Classification of Lichens 
125 
studied attack the cells of the algal hosts directly ; and in such 
instances the algal cells or filaments are so modified or broken up 
that the nature of the algal host is difficult or impossible to ascer- 
tain. But where the union of hyphae with algal-host cells can 
not be seen, the latter are little, if at all, modified. In this con- 
nection, it may be added that Bornet saw his algae growing in 
the usual form and also modified by the lichen parasites, and so 
established that the modification is not phylogenetic but comes 
about rapidly. He referred his algal hosts to the genera Trente- 
pohlia, Phyllactidium, Chlorococcum, Pleurococcus, Dactylococ- 
ciis, Ulothri.r{?) , Cladotlinx{?) , Scytonema, Nostoc and Oscil- 
latoria. These are nearly all cosmopolitan algae, to be expected 
on barks, earth, bases of mosses and in cracks and crevices where 
lichens may begin development from spores and attack their algal 
hosts. 
Treub (135) caused lichen spores to germinate in pure cultures 
in the hope that he might develop the green cells from the hyphae. 
Of course he failed in this. Then he made cultures from spores 
of Xanthoria parietina (L.) Th. Fr., Ramalina calicaris (L.)iFr., 
Lccanora siibfusca (L.) Ach. znd Physcia pidverulenta (Schreb.j 
Nyl., with the algae present and found that the germ tubes of the 
spores lay hold on the algae. He used wild Chlorococcum humi- 
cola and obtained the same results as when he took the algae 
from lichen thalli. He thus proved that the germinating spores 
may readily attack free algae, as would be inferred from the fact 
that lichens so frequently grow in the vicinity of the free algae. 
He got the hyphae to branch freely after attacking the algae, but 
did not get fully developed thalli. Borzi (34) made cultures of 
Physcia pulverulenta (Schreb.) Nyl., Physcia ciliaris (L.) Ach., 
Xanthoria parietina (L.) Th. Fr. and Pertnsaria communis Lam. 
& DC. with algae, and concluded that these lichens are Ascomy- 
cetous fungi and are parasitic on the algae with which they grow. 
As briefly outlined above, Moller (89) found a small white 
thelephore growing with the lichen, Cora. The fungus rarely 
occurs elsewhere than on the same substratum and in the same 
locality with this lichen. The general structure is the same in 
both plants, and their spores behave alike in germination. He 
