THE LICHENS 



373 



Small flask-shaped antheridia, here known as spermogonia, are formed 

 on the surface of the thallus, and these produce great numbers of unicellular 

 spermatia, that is, non-motile male cells. The spermatia are shed simul- 

 taneously in slimy masses. Each spermatium has a cell wall, unlike the 

 corresponding structure in the Rhodophyceae, but they are apparently 

 functional as they are found adhering to the trichogynes, with the terminal 



Paraphyses » 



Ascus -" 



Hymenium m . \ *«m 



Fig. 359. — Peltigera canina. Part of a section through 

 the hymenium of an apothecium showing large 

 asci containing elongated ascospores, and para- 

 physes which are united above to fomi a covering 

 layer known as the epithecium. 



cell of which their contents fuse. After fertilization the cells of the tricho- 

 gyne collapse and ascogenous hyphae are produced from the ascogonium, 

 and from them the asci develop in a way entirely comparable with that 

 in an Ascomycete, like Pyronema (Fig. 359). The details of the nuclear 

 process are not entirely understood. In some Lichens both the trichogyne 

 and the spermatia are absent, and in such cases the ascogonium develops 

 parthenogenetically. 



Reproduction in the Pyrenocarpeae 



Verrucaria margacea is an interesting aquatic Lichen growing on stones 

 in running water. The young thallus is pale green, but it becomes dark olive- 

 brown and almost black with age. The algal constituent is a form of 

 Pleiirococcus. The fungus forms a compact pseudoparenchymatous network, 

 absolutely uniform in structure throughout the thallus. The perithecia are 

 immersed in elevations of the thallus and are characterized bv a firm black 

 peridium. Paraphyses line the inside of the ostiole and the upper portion 



