I. THE MEANS OF PROPAGATION AND DIS- 
PERSAL OF THE ICELAND LICHENS. 
Ne 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, 
Soredia, 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 aculeata, C. cucullata, C. 
hiascens, C. nivalis, Nephroma spp., some Peltigera spp., Physcia pul- 
verulenta v. muscigena, 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 
