156 OLAF GALL0K 



Alectoria divergens Ach. Cladonia pityrca. 



jubala L. pyxidata. 



nigricans Nyl. rangiferina. 



ochroleuca Nyl. rangiformis. 



Cetraria aculeata Fr. turgida. 



Cladonia amaurocrsea. uncialis. 



bellidiflora. verticillata. 



cariosa. (Polychidium muscicolaSw.,dwarl- 



coccifera. formed). 



decorticata. Sphserophorus fragilis L. 



fimbriata. Stereocaulon condensatum Hoil'm. 



Floerkeana. incrustatum Flk. 



foliacea. paschale (L.) Fr. 



f'urcata. tomcntosum(Fr.)Th. Fr. 



gracilis. Thamnolia vermicularis Schaer. 



These and numerous other species have been specially treated 

 in "Forberedende Undersogelser" (1013), 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, a 

 jtriori, we might be tempted to believe, that the lichen-hypha? 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, Fu is ting, Stein er, 

 Zukal, Zahlbruckner, Hulth, Bachmann, Funfstuck, Lang, 

 Friederich and Stahlecker. 



The researches of these investigators have proved that there is 

 a distinct anatomical difference between lichens from primitive rocks, 



