LICHENOLOGY OF ICELAND 131 



propagation, soredia or detached portions of thallus, are extremely 

 common. This is the case for instance with Alectoria and several 

 Cladonia spp. Here there undoubtedly also exists a certain correla- 

 tion between these means of propagation, vegetative means of pro- 

 pagation in several species being of far greater importance for the 

 dispersal of the species, than ascospores. This phenomenon of vege- 

 tative propagation is known from several places; thus in Denmark 

 Cladonia rangiferina is sterile as a rule, and is most frequently pro- 

 pagated there by detached portions of podetia, and the same is the 

 case with Cladonia nncialis, etc.: this circumstance, however, has 

 been^exhaustively discussed by me previously (Gall0e, 1913, p. 41, 

 and under the different species in the same paper). As regards 

 Thamnolia vermicularis, it never forms apothecia. 



As to how the ascospores escape from the ascus and their mode 

 of dispersal, are but little known. There is much which goes to 

 show that in the majority of species the spores are dry bodies, 

 which are carried away by the wind and thereby dispersed. But it 

 is just possible that in some of the species they are sticky, and 

 require other means of dispersal. 



Pycnoconidia. At present very little is known as regards 

 the extent to which pycnoconidia occur among the Crustaceous, 

 Foliaceous and Fruticose Lichens, nor is it known what role they 

 play as regards propagation. They have been regarded both as male 

 reproductive cells, and as vegetative means of propagation. In some 

 cases, investigators have succeeded in producing the lichen-thallus 

 by bringing together pycnoconidia and gonidia in a pure culture, 

 that is, have succeeded in propagating lichens vegetatively by pycno- 

 conidia; this, however, does not necessarily compel us to regard 

 the pycnoconidia of all species as vegetative means of propagation. 



To regard pycnoconidia as male reproductive cells, is perhaps 

 more disputable; their importance as such has not at any rate been 

 proved; their entire biological importance is consequently rather 

 problematic. To make investigations regarding this point will, no 

 doubt, well repay the trouble. According to what has just been said, 

 nothing can be stated at the present time as to whether there exists 

 any correlation between the occurrence of pycnoconidia and the 

 occurrence or absence, respectively, of other means of propagation. 



Soredia, as is well-known, are small bodies which consist 

 partly of hyphae and partly of gonidia, and are formed sometimes 

 in quite accidental places the on thallus, sometimes in fairly well- 



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