41 6 DIVISION III. MODE OF LIFE OF THE FUXGI. 



"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, e,/]. 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 , Korber's Naetrocymbe, 

 and Atichia 2 . 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 

 in its thallus. Both species live on the 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 3 , 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. Verhalln. einiger Krustenflechten in Conn's Beitr. z. Biol. II. 



2 See Millardet, as cited on page 262. 



s See Botaniska Notiser, 1876, No. 6 a. Also Just's Jahresber. 1875, p. 105. I have not been 

 able to consult the paper Allelotismns in K. norske Vid. Selsk. Skrifto. VII, 1872. 



