154 
Mycologia 
grow on calciferous rocks. He thought that the oil must be 
produced with little regard to the amount of lime in the sub- 
stratum, while Fiinfstuck, who regarded the oil a waste product, 
failed to find it in considerable quantity, except in lichens that 
grow on calciferous rocks. Bachman agrees with Zukal, while 
Friederich and Stahlecker agree with Fiinfstuck. Those who 
regard the oil a reserve food, think that it is* most abundant about 
the time that the lichen fruits begin to form, while Fiinf stuck 
found it quite as abundant at other times and in lichens that pro- 
duce little or no fruit. 
Bachmann (ii) also worked on the lichens on silicious rocks 
and found that the rhizoids usually penetrate through the mica 
particles of granites, commonly passing between the lamellae, but 
sometimes passing through them. He found the oil-bearing 
sphaeroidal cells, but performed no careful chemical analyses to 
prove that lime is not present in some of these rocks in sufficient 
quantity to account for their presence. As stated above, Bach- 
mann concluded that lichens do not attack quartz and silicates 
chemically ; but it has been proved that they or their algal hosts 
secrete acids which do corrode these rocks so that the lichen 
hyphae penetrate into them. It is certain that moisture, oxygen, 
carbon dioxide and carbonic acid are rather abundant about 
lichens because of the nutritional processes of the lichens and 
their algal hosts, and one or more of these agents will dissolve 
any rock. 
Stahlecker (125) subjected rocks to careful chemical analysis 
and found that ordinary statements about the character of rocks 
on which lichens grow are very unreliable, and that there is really 
a close relation between the oil secretion and the amount of lime 
and magnesia present in the rocks. Friederich (59) ascertained 
that lichens attack all rocks, but lay hold on the more basic por- 
tions sooner than the more acid. This would account for finding 
certain portions of granites attacked and others left bare for a 
time, but does not warrant the conclusion of Bachmann that some 
rocks are not attacked at all. 
In general, the more the lichen penetrates into the rocks the less 
numerous are the algal host cells, and the less the penetration into 
the rock, the more abundant the algal cells. So the quartz and 
