FUNGI. 



271 



which becomes surrounded by a very delicate membrane and grows outwards in the 

 form of a filament (Fig. 194, -^, 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 

 thallus as the apothecia. There are cavities in the thallus (Conceptacles), 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 



Fig. 194.— Lichen-spores germinating; A longitudinal section of a spore oi Pertusaria communis after lying 34 hours in 

 glycerine, s the first start of the germinating filaments ; B spore of Pertusaria leioplaca with a number of germinating 

 filaments (after Ue Bary, X390) ; C germinating septate spores oi Solorina saccata (after Tulasne). 



a fine orifice in the spermogonium. Sometimes also conceptacles are found in which 

 larger structures, more like spores, are detached from the sterigmata; receptacles of 

 this kind are called Pycnidia. The signification of both is at present unknown. 



Besides the spores, most Lichens also possess organs of a very great reproductive 

 power, the Soredia. This term is applied to single gonidial cells or groups of gonidia which, 

 surrounded by a weft of hyphae, are pushed out of the thallus, and are able, without any 

 further process, to grow into a new Lichen-thallus. The soredia are produced from the 

 thallus in the non-gelatinous Lichens as a fine powder, forming sometimes dense pulvinate 

 masses (as in Usnea, Ramalina, Evernia, Physcia, Parmelia, Pertusaria, &c.). In the 

 heteromerous thallus the soredia appear in the gonidial layer ; single gonidia, or some- 

 times several together becoming woven over by branches of hyphae which cling closely to 

 them and form an envelope of fibres. The gonidia divide repeatedly, and each daughter- 

 cell is again woven over. This process is often repeated, the soredia accumulate in 

 great numbers in the gonidial zone, and finally rupture the cortex. After escaping in 



