LICHENOLOGY OF ICELAND 133 



to be a very common means of propagation, and to occur where 

 apothecia are rare, or not very frequent, (e. g. Cladonia fimbriata, 

 Ramalina subfarinacea and Usnea melaxantha). The soredia are dis- 

 persed by the wind, or perhaps by adhering to the hair of animals. 



Detached portions of thallus as a means of propagation 

 are not known to occur with any certainty in a single Crustaceous 

 Lichen. It is probable that this happens in the above-mentioned 

 Foliaceous Lichens. In the Fruticose Lichens it has been 

 demonstrated with certainty in several earth-lichens (Cladonia, etc., 

 for instance Cladonia rangiferina, uncialis, rangiformis, etc.). In 1913 

 I fully mentioned and figured it in several species. It appears to 

 be a very important and widely distributed means of propagation 

 in several species, and largely replaces propagation by ascospores, 

 which in such species usually occur rather rarely. 



Dispersal takes place no doubt both by the agency of the wind 

 and of animals. 



If we consider the way in which lichens may be assumed to 

 have been dispersed in Iceland itself, we must understand clearly 

 that ascospores, pycnoconidia, soredia, and detached por- 

 tions of thallus are, as far as we know at present, generally dis- 

 persed by the agency of the wind. But animals also no doubt, 

 more or less, play their part in it. It may be regarded as certain 

 that almost all animals that wander about in Iceland occasionally 

 get lichen-spores, portions of thallus, etc. attached to them. Sheep 

 that roam about almost everywhere, undoubtedly play no small role 

 as disseminators, and the same, I dare say, applies to the majority 

 of the other terrestrial animals, wild as well as tame. How far means 

 of propagation such as ascospores and pycnoconidia, after having 

 passed through the digestive organs of lichen-eating animals (sheep 

 and reindeer), retain their power of germination, is not known in 

 any single instance. Here, as everywhere in the lichen-biology, we 

 stand at the present time just at the stage of asking questions, with- 

 out as yet having got very many of them answered, because lichen- 

 ologists do not, on the whole, occupy themselves with biological 

 problems. But in a general way it may be said that species which 

 play any essential part as articles of food for animals, namely the 

 larger shrub-like earth-lichens, are generally little dispersed by asco- 

 spores, for they bear fruit rather sparingly, as mentioned above. 



