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 uncialis, etc.: this circumstance, however, has 
been exhaustively discussed by me previously (Galloe, 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 rôle 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 hyphæ and partly of gonidia, and are formed sometimes 
in quite accidental places the on thallus, sometimes in fairly well- 
9* 
