134 OLAF GALLOE 
Species such as Cladonia rangiferma, Alectoria ochroleuca, Cetraria 
aculeata, and Alectoria nigricans are undoubtedly far more frequently 
propagated by detached portions of thallus, some carried away by 
the wind, and others adhering to the body of animals. 
That portions of thallus should be able to pass through 
the digestive organs of animals uninjured, is a priori improbable, 
— if such were the case, they would be rather useless as fodder! 
Any possibility of such dispersal by means of herbivorous animals, 
is thus scarcely possible. 
But water, also, plays a part in the dispersal of lichens, By 
the agency of water, the submerged Verrucaria spp. which live along 
the coasts, are undoubtedly dispersed. Then it is probable that the 
lichens which occur by water-falls, part of which live washed by 
the falling water (for instance Staurothele clopima), are dispersed 
by the downward-flowing water. 
If we now consider the agencies which play or have played a 
part in the exchange of lichen-species with the surround- 
ing countries, we must, as in the case of dispersal in Iceland 
itself, point out three different agencies: wind, water and animals. 
The lichens which may be assumed to have immigrated, (re- 
spectively emigrated,) by the agency of the wind, are firstly all 
those that propagate by ascospores, consequently, practically all 
the crustaceous lichens, at any rate, by far the greater part of the 
species (about 65 °/o); then next, the majority of the foliaceous lichens, 
possibly all of them (there are altogether about 21 °/o of them); and 
lastly some fruticose lichens. As regards the latter, however, it must 
be taken for granted, that at least Thamnolia vermicularis did not 
migrate in the form of spores, as it never bears fruit. 
Some of the species have probably also migrated by means of 
pycnoconidia, but as the occurrence of the latter in the species 
is very incompletely known, and as their importance as a means 
of propagation may be disputed, it is not possible to form any 
opinion as to what importance they are of or have been, in respect 
to immigration. 
Lastly, some species have migrated as soredia. As mentioned 
above the soredium is not a very common means of propagation 
in the Icelandic species; in the crustaceous lichens it is extremely 
rare. I am not prepared to state with any certainty in how many 
