Fink: Classification of Lichens 
153 
probably able to form this substance in the process of carbon 
assimilation; hence, the surface of the rock would, in time, be- 
come corroded so that the lichen hyphae could penetrate into it. 
Bachmann (12, 13) has since concluded that lichens neither cor- 
rode nor penetrate into quartz or silicates; but Stahlecker (125) 
proved by careful obsen^ation that lichen hyphae will penetrate 
into all rocks, after they have been corroded as explained above. 
Zukal (149, 150) studied the sphaeroidal cells and the enlarged 
hyphae found in lichens on calciferous rocks. By subjecting 
these structures to careful chemical treatment, he ascertained that 
they contain a fatty oil similar to that found commonly in fungal 
spores and sclerotia. He decided that the oil must be a reserve 
food supply elaborated by the algal host. Fiinfstuck (63), by 
removing the algal host and the upper portion of the lichen thallus 
from the rock, proved that the hyphae still remaining in the rock 
continue to grow for two or three years without the algal host and 
produce the sphaeroidal cells and the enlarged oil-bearing hyphae 
as well as before. He thus proved positively that the algal host 
plays no part in the oil production, and decided that the oil is not 
a food but a waste product, of no use to the lichen. He has 
proved the first point, but not the second. 
Bachmann (8, 9, 10) studied the relation of certain lichens to 
the dolomite and the limestone on which they grow, by dissolving 
fragments of the rock and by grinding pieces of rock into thin sec- 
tions, in which the lichen and its algal host cells could be seen. 
He found that these lichens of calciferous rocks are usually hy- 
polithic, only the fruits showing at the surface. The lichens he 
found to penetrate from 200 to 12,000 or 14,000 mic. into the 
rock, while the algal cells reach depths of 100 to 500 mic. Each 
algal group is surrounded closely by lichen hyphae; but neither 
Bachmann nor other workers has found out more regarding the 
relation of the lichen to the algal host in these or other rock- 
inhabiting lichens. The hyphae eat their way into the rock 
without respect to structure, passing through crystals of various 
forms and sizes. In support of the belief that the oil is 
reserve food, Zukal claimed that lichens that grow on bark, on 
earth and on rocks devoid of lime or magnesia contain the same 
kind of fatty oil, sometimes in as great abundance as those that 
