LICHENOLOGY OF ICELAND 143 



The subterranean thallus normally is free of gonidia (barring 

 foreign-gonidia). It may be very strongly developed, and it pushes 

 its way down among the particles of soil, which may gradually 

 become entirely enclosed by its hyphse. I have sometimes observed 

 shapeless enclosed lumps of black humus (Lecidea decolorans, Bi- 

 limbia sabiiletorum (D. Lik. 0., pi. 4, fig. 15), Bacidia citrinella), some- 

 times organic remains with the cell-structure preserved (Lecidea de- 

 colorans), and sometimes grains of mineral matter (Buellia scabrosa). 

 In no case has it been possible to demonstrate whether solution 

 takes place by the agency of the licheh-hyphse. It is almost incom- 

 prehensible that something of this kind should not happen, but it 

 has not been proved. It is possible that what is set free of the 

 enclosed organic remains, or of the mineral grains by purely che- 

 mical decomposition, suffices for the lichens. 



In some few cases (Lecidea decolorans (I). Lik. 0., pi. 10, fig. 53, c), 

 Pannaria brunnea) I found, enclosed in the subterranean thallus, an 

 undetermined species of green algse. The gonidia were dead and 

 decoloured, but the lichen-hyphae had not sent haustoria into them 

 (nor do they do so as a rule to their normal gonidia). The death 

 of the gonidia was undoubtedly due to contact with the hyphse, 

 and possibly some use had been made of their contents. The whole 

 thing must be regarded as a Cephalodium-formation, a "hypogaean" 

 cephalodium or perhaps a "pseudocephalodium." 



About the mode of propagation of the crustaceous lichens very 

 little is known. Ascospores, perhaps pycnoconidia, are probably their 

 most common means of propagation, I have not observed soredia 

 or detached portions of thallus in them, as in the fruticose lichens. 

 It is a very interesting fact, that these means of propagation appear 

 to be at any rate rare in the primitive, crustaceous lichens. 



Crustaceous lichens are very weak in competition with other 

 plants, as these easily cover them over and exterminate them. They 

 are most favourably situated in Iceland, and in other Arctic coun- 

 tries; this will be discussed more fully below. 



Iceland has the following crustaceous earth-lichens: 



Bacidia arceutina Ach. Baeomyces byssoides (L.) Th. Fr. 



caudata Nyl. placophyllum \Vahlenbg. 



flavo-virescens Dicks. Buellia badia Koerb. 

 herbarum Hepp. parasema (Ach.) Th. Fr. 



milliaria Fr. scabrosa Koerb. 



obscurata (Sm.) Th. Fr. Caloplaca cerina (Ehrh.) Th. Fr. 

 squalescens Nyl. Jungermanni3e(Vahl)Th.Fr. 



