158 OLAF GALLGE 
devoid of gonidia, which is sunk into the substratum and which 
corrodes the individual grains of mineral matter. According to A. 
Friederich this hyphal layer is thin in the silicicolous lichens, 
and cannot at all be compared, as regards size, with the corres- 
ponding tissue in the calcareous lichens. Besides, according to 
Friederich, it is never furnished with oil-hyphe or spheeroid- 
hyphe; but according to Bachmann, such are said to occur. At 
any rate, Fünfstück’s investigations show that where the same 
lichen grows both on calcareous and on siliceous rocks, the indi- 
viduals from the calcareous rocks contain oil, while those from the 
siliceous rocks do not. Fünfstück, whose results have since been 
strongly supported by E. Lang’s renewed investigations, appears 
to differ somewhat from Bachmann as regards the occurrence of 
oil-hyphæ in the silicicolous lichens; this disagreement need not, 
however, be a fundamental one, as there will probably be various 
degrees with regard to the oil-contents connected with the larger or 
smaller amount of lime contained in the rock-species in question. 
At any rate, it is certainly an undisputable fact that the amount of 
oil is greatest in the calcareous lichens. 
The biological importance of the oil-contents is much contested. 
Zukal is of opinion — but quite wrongly, according to Fünf- 
stiick’s investigations, — that the oil is a supply stored for fruit- 
setting. Hulth also, regards the oil-containing tissue as reservoirs 
for reserve food-material. Fünfstück shows that there exists no 
connection between the fruit-setting and the oil-contents, and is of 
opinion, that the oil is an excretion formed owing to the accumula- 
tion of the carbon dioxide, which is set free by the hyphæ pene- 
trating into the calcium carbonate. 
As mentioned by Bachmann and Stahlecker the hyphæ 
affect the mineral grains in various ways. According to Stahlecker 
they corrode quartz. This is denied by Bachmann. Basic mineral- 
grains are affected before the acid mineral-grains, according to Stahl- 
ecker. When there is a decided cleavage-plane in the mineral-grains 
(as in mica), the hyphe, according to Bachmann, follow the di- 
rection of the cleavage, whereby the existing cleavages are widened 
and filled with hyphæ. 
The epilithic part of the thallus contains gonidia. It frequently 
consists of a growing lichen-mycelium produced centrifugally from 
the centre of germination, bearing on the thallus numerous small, 
rounded or irregularly angular areas containing gonidia; according 
