326 



THALLOPHYTES. 



on which the spore is placed. The mode of germination of the very large spores of 

 some genera, Megalospora, Ochrolechia, and Pertusaria, differs from that of all the rest. 

 They are simple, not septate, and densely filled with drops of oil (Fig. 220, A, B). Each 

 spore puts out from different parts of its circumference a great number, even as many as 

 a hundred, germinating filaments. The formation of each begins with the appearance 

 in the endospore of a cavity widening from within outwards, which becomes sur- 

 rounded by a very delicate membrane and grows outwards in the form of a filament 

 (Fig. 220, A,B). 



Besides the apothecia with ascospores capable of germination, Spermogonia are also 

 generally present in Lichens, as in Ascomycetes ; they generally occur on the same 



FIG. 220.— Lichen-spores germinating ; A longitudinal section of a spore oi Peitusarui commtcnis &iter lying 34 hours 

 in glycerine, s the rudiments of the germinating filaments ; B spore oi Pertusaria leioplaca with a number of germinating 

 filaments (after De Bary, x 390) ; C germinating septate spores of Solorina saccata (after Tulasne). 



thallus as the apothecia. They are cavities in the thallus which are globular, flask- 

 shaped, or sinuous, and densely clothed and almost filled with sterigmata ; from these 

 sterigmata the spermatia are detached in very large numbers, and escape through a 

 fine orifice in the spermogonium. Sometimes also receptacles are found in which larger 

 bodies, more like spores, are detached from the sterigmata ; receptacles of this kind are 

 called Pycnidia, as in the Pyrenomycetes. 



Besides the spores, most Lichens also possess organs termed Soredia, by which they 

 are very extensively reproduced. They are single gonidial cells or groups of gonidia 

 which, surrounded by a weft of hyphge, are pushed out of the thallus, and are able, 

 without any further process, to grow into a new Lichen-thallus. The soredia are pro- 

 duced from the thallus in the non-gelatinous Lichens, as a fine powder, forming sometimes 



