LK.HENOLOGY OF ICELAND 159 



to Friederich, these gonidia-areas have come into existence in 

 places where the gonidia (algae) have accidentally fallen on the 

 lichen-mycelium. According to Stall lecker each area has originally 

 been an independent thallus, which, by coming into contact with 

 similar neighbouring thalli, forms with these a "Gesamtthallus," 

 which may afterwards grow as a unity, starting from a common 

 centre. This interpretation sounds quite incredible, and I think it 

 is very rarely, if ever, in accordance with fact. Can it, on the whole, 

 be understood that these smaller thalli are "independent," as they 

 have all been produced by the same lichen-mycelium? 



It is quite another question, whether a group of really indepen- 

 dent thalli, produced each from its own ascospore, on meeting, can 

 alter and carry on a joint growth. About this nothing is known, a 

 priori, it does not seem very probable. 



In reality, these small thallus-patches containing gonidia, men- 

 tioned by Stah lecker, must quite naturally be regarded as ana- 

 logous, for instance, to the primary scales in Cladonia, which are 

 also small green gonidia-containing thalli on a common mycelium; 

 or with the exactly corresponding balls of gonidia in numerous 

 crustaceous earth-lichens (Lecidea alpestris, L. uliginosns, etc.). 



Quite another separation into patches may moreover take place 

 by existing patches splitting asunder into separate parts by growth- 

 tensions (or by drying?) (see "Dan. Lik. 0k.," fig. 19, a, b, c, d). 



When the thallus is smooth and non-partitioned, Stahlecker 

 is of opinion that it is an old, formerly partitioned thallus. I can- 

 not believe this interpretation of the condition. 



Friederich has found the gonidia-layer of the silicicolous 

 lichens to be thicker than that of the calcareous lichens, Funf- 

 stiick has also found this to be the case. 



The mode of propagation has been investigated by Bee km an n, 

 who found that some species (Lecanora badia, L. cenisea), the thalli 

 of which are partitioned, ma} 7 reproduce by means of detached 

 portions of the thallus, whereas soredia are absent. On the other 

 hand, the partitioned thalli of the Rhizocarpon spp. do not appear 

 to be able to reproduce in this way. 



Thin, cohering (non-partitioned) thalli do not appear to be able 

 to reproduce in this way. Whether this mode of propagation, on 

 the whole, plays any important part in nature, compared with pro- 

 pagation by spores, I regard as doubtful. 



With regard to capacity for competition, the crustaceous lichens 



