156 OLAF GALLOE 
Alectoria divergens Ach. Cladonia pityrea. 
= jubata L. — pyxidata. 
— nigricans Nyl. — rangiferina. 
— ochroleuca Nyl. = rangiformis. 
Cetraria aculeata Fr. — turgida. 
Cladonia amaurocræa. — uncialis. 
— bellidiflora. — verticillata. 
— cariosa. (Polychidium muscicola Sw., dwarf- 
— coccifera. formed). 
— decorticata. Sphærophorus fragilis L. 
— fimbriata. Stereocaulon condensatum Hoffm. 
— Floerkeana. — incrustatum FIk. 
— foliacea. — paschale (L.) Fr. 
— furcata. — tomentosum (Fr.)Th. Fr. 
— gracilis., Thamnolia vermicularis Schaer. 
These and numerous other species have been specially treated 
in "Forberedende Undersøgelser” (1913),-to which the reader is 
referred. 
4. ROCK LICHENS. 
When the climatic conditions are favourable to the growth of 
lichens, a lichen-vegetation may eventually develop on a rocky sub- 
stratum. But other demands also must be satisfied, namely those 
which have regard to the physical and chemical conditions of the 
substratum. 
Many different rocky substrata may be distinguished, and some 
differences in their lichen-vegetation may also be pointed out. 
The most important physical conditions are, as far as is known, 
the following: — 
Stahlecker has observed that on stratified rocks lichens first 
choose those surfaces which are perpendicular to the stratification. 
How this phenomenon is to be explained is yet unknown but, à 
priori, we might be tempted to believe, that the lichen-hyphæ more 
easily penetrate the rock parallel with the stratification, than trans- 
verse to it (compare with this the fact that wood-lichens are best 
able to grow parallel with the “fibres” of the wood). Perhaps such 
surfaces disintegrate also more quickly. 
The importance of the chemical conditions are far better known, 
owing to investigators like Krempelhuber, Fuisting, Steiner, 
Zukal, Zahlbruckner, Hulth, Bachmann, Fünfstück, Lang, 
Friederich and Stahlecker. 
The researches of these investigators have proved that there is 
a distinct anatomical difference between lichens from primitive rocks, 
