II. THE MEANS OF PROPAGATION AND DIS- 

 PERSAL OF THE ICELAND LICHENS. 



Ater having considered, in the above, the composition of the 

 Flora, the next point to be investigated is, by which means 

 of propagation we can imagine that the species have been dispersed 

 over the island, and have immigrated from the surrounding coun- 

 tries into Iceland, and vice versa. 



Lichens are propagated by Ascospores, Pycnoconidia, 

 Sored ia, and detached portions of thallus. 



Ascopores must be assumed to be the original means of pro- 

 pagation, which, as we know', has been handed down directly from 

 the prototypes of the lichens, the Ascomycetes. Those lichens which 

 still stand on a low, primitive phylogenetic stage, viz. the Crusta- 

 ceous Lichens, have still, almost all, as a rule more or less 

 numerous apothecia, usually with numerous well-developed spores. 

 In the synoptic list of the chief biological conditions of the lichens 

 of Iceland (see below) it will be seen that all the crustaceous lichens 

 have been, and as a rule will be, found with apothecia. Among 

 the Foliaceous Lichens there are several which often occur in 

 great abundance, but are nevertheless rarely found with apothecia. 

 This is for instance the case with Cetraria acnleata, C. cucnllatd, C. 

 hiascens, C. niualis, Nephroma spp., some Pelliyera spp., Physcia pnl- 

 vernlenta \. innscigena, and perhaps a few other species. As will be 

 seen, it is all the leaf-shaped earth-lichens which can undoubtedly 

 be propagated by detached portions of thallus, which; when the 

 plant is in a dry condition, are widely dispersed by the wind, or 

 perhaps also, in part, by animals; but no thorough investigations 

 are to hand as regards this point. What has been said of the foli- 

 aceous lichens is also frequently the case among the Fruticose 

 Lichens, namely, that apothecia are rare, while other means of 



