Fink : Classification of Lichens 
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pohlia, the alga being parasitized later. The algal host enters the 
thalli from without. Then the thallus grows more luxuriantly 
and sometimes becomes partly epiphloeodal, though entirely hy- 
pophloeodal before parasitizing the alga. The lichen hyphae 
attack the Trente pohlia alga filaments, render them unrecognizable 
by breaking them up into shorter filaments or into single cells, 
and then according to Frank, bore into the cell contents of the 
individual cells. Whenever colonization fails, no apothecia are 
formed, the lichen (?) dying without fructifying. Frank found 
assentially the same condition in our common Graphis scripta (L.) 
Ach., which sometimes grows for a time outside the parasitic re- 
lation. He also found that Arthonia disperse (Lam. & DC.) Dub. 
A. punctiformis Ach., Arthopyrenia cerasi Koerb. and A. rhy- 
ponta Mass, never enter into the parasitic relation with algae, the 
technique used showing no algae growing with any of these so- 
called lichens at any time. Frank studied only a few of the many 
similar lichens, and such tardy entrance of many of these plants 
upon the parasitic relation or entire failure to enter into this 
relation can scarcely be so rare as is claimed by those who ad- 
here to the mutualism theory or some modification of it. These 
lichens and lichenoid plants are by no means rare and must be 
dealt with in any consideration of the relation of the lichen to its 
algal host. Frank found that the cells of the Trent epohlia fila- 
ments, when parasitized, show much thinner walls than when not 
parasitized, while the chlorophyll is absent or poorly developed. 
The oil globules are absent or of a golden or orange red color, 
while they are an intense rust red color in the free algae. He 
decided that the algal filaments bore through intact periderm as 
well as enter through cracks, and that these entering filaments 
arise from zoospores which come to rest and germinate on the 
surface. He thought that the alga bored into the periderm only 
over lichen thalli; but this can hardly be true since Trentepohlia 
filaments commonly occur in the periderm where no lichens are 
growing. He observed that the alga resumes its usual form 
soon after the death of the lichen parasite. 
Lindau (8i) found that the points of contact between the 
hyphae of hypophloeodal lichens and the Trentepohlia filaments 
are comparatively few, and that no haustoria are formed. So 
