416 DIVISION III-—MODE OF LIFE OF THE FUNGI. 
the fissure as a powdery mass loosely held together by the hyphae of the thallus, 
which are drawn out with it. These powdery and easily dissipated accumulations of 
the separate bodies which have now been described are termed by Schwendener 
soredia-heaps or sort, and it will be well to retain his terminology, though the word 
soredium was originally applied to the whole heap. 
A soredium can give rise to an unlimited number of new soredia in the manner 
just described after a sorus has emerged from the rind, and even after the soredia 
have separated from one another and been dispersed as dust. This uniform 
multiplication leads to the formation of layers and accumulations of soredia which are 
not unfrequent in shaded spots, as in the case of Physcia parietina. Where the 
conditions are favourable to vegetation a thallus is formed and fully developed from 
them (see Fig, 181, ¢, 7). Such a thallus may even be frequently produced in Usnea 
according to Schwendener on the parent-thallus, forming soredial branches which 
remain firmly united to it. 
Excessive development of roundish soredia-heaps with a remote resemblance to 
apothecia on a crustaceous or foliaceous thallus, on which apothecia are not at the 
same time produced, gives rise to the forms on which Acharius has founded his 
pseudo-genus Variolaria. 
Pseudo-lichens. The above account necessarily excludes from the class of Lichens 
those forms which are ranked with them in our books because they have been collected 
by Lichenologists, but which do not possess the one mark of the true Lichen, namely, the 
presence of Algae in their thallus. Among these are the Celidieae, Abrothallus and 
others, which are parasitic on the thallus of Lichens, the genus Myriangium mentioned 
above on page 107, the Arthopyrenieae examined by Frank 1, Körber’s Naetrocymbe, 
and Atichia®. All these forms except the last are simple Ascomycetes ; Atichia, according 
to Millardet’s able investigations, is a Fungus of uncertain position which forms clustered 
spore-groups. Those species also will of course be excluded which have been placed in 
the same genus with others having the true Lichen-thallus, and are really nearly related 
to them but have not the mode of life of a Lichen. Frank found that Arthonia vulgaris 
has the Lichen-thallus (see on page 399), but Arthonia epipasta, Kbr. has only hyphae 
inits thallus. Both species live onthe bark of trees ; the former is a Lichen-fungus with 
that habitat, the latter simply a saprophytic Fungus. There is nothing strange in this, 
for there are natural genera in other parts of the system, in which some of the species 
are usually parasitic, while others are adapted to a saprophytic mode of life, for example 
Sclerotinia. Norman’s Morioleae (Moriola, Spheconisca) also appear to me, from the 
descriptions which I have read of them}, to be to say the least doubtful Lichens ; they 
deserve further investigation. If they really have Algae in their thallus, they are 
simply Lichens which have also the power of inclosing parts of Liverworts, pollen-grains 
and probably other strange bodies in their thallus. 
Historical notice of the Lichens. It is well known that the views of botanists 
respecting the thallus of the Lichens up to the year 1868 were not those which have been 
given in the preceding pages. It was supposed to be a body whose constituent parts all 
proceeded from one another, and ultimately from the germinating spore ; the algal cells 
especially, so far as any clear conception had been formed about them, were regarded as 

1 Biol. Verhaltn. einiger Krustenflechten in Cohn’s Beitr. z. Biol. II. 
2 See Millardet, as cited on page 262. 
® See Botaniska Notiser, 1876, No. 6a. Also Just’s Jahresber. 1875, p. 105. I have not been 
able to consult the paper Allelotismus in K. norske Vid. Selsk. Skrifto. VII, 1872. 
