332 SYSTEMATIC 



In some of the genera the lichen hyphae travel within the gelatinous 

 sheath of the filaments, both algae and hyphae increasing by apical growth 

 so that filaments many times the length of the alga are formed as in 

 Ephebe. In others the filaments scarcely increase beyond the normal size 

 of the alga as in Thermutis (Gonionema); or the gelatinous algal cells may 

 be distributed in a stratum of hyphae. 



The apothecia are minute and almost closed ; they may be embedded 

 in swellings of the thallus, or are more or less superficial. The spores are 

 rather small, colourless and simple or I -septate. 



The lichens of this family are rock-dwellers and are mostly to be found 

 in hilly or Alpine regions. A tropical species, Leptogidiwn dcndriscnm, occurs 

 in sterile condition in south-west Ireland. There are few species in any of 

 the genera. 



Algal cells Scytonema. 



Thallus minutely fruticose, non-corticate i. Thermutis Fr. 



Thallus minute, of felted filaments, cortex one) ... . 



, . > 2. *Leptodendnscum Wain. 



Thallus of elongate filaments, cortex of several cells 3. Leptogidium Nyl. 



Thallus foliose or fruticose, cellular throughout 4. Polychidium Ach. 



Thallus crustaceous, non-corticate 5. Porocyphus Koerb. 



Algal cells Stigoncma. 



Thallus minutely fruticose, non-corticate 6. Spilonema Born. 



Thallus of long branching filaments. 



Spores septate ; paraphyses wanting 7. Ephebe Fr. 



Spores simple; paraphyses present 8. Ephebeia Nyl. 



Thallus crustaceous; upper surface non-corticate,) 



\ 9. *Pterygiopsis Wain, 

 lower surface corticate J ' 



XXXVII. PYRENOPSIDACEAE 



In this family are included gelatinous lichens of which the gonidium is 

 a blue-green alga with a thick gelatinous coat, either Gloeocapsa (including 

 Xantliocapsd) or Chroococcus. In Gloeocapsa and Chroococcus the gelatinous 

 envelope is often red, in Xantiiocapsa it is yellow, and these colours persist 

 more or less in the lichens, especially in the outer layers. 



The thallus is in many cases a formless gelatinous crust of hyphal 

 filaments mingling with colonies of algal cells as in Pyrenopsis; but small 

 fruticose tufts are characteristic of Synalissa, and larger foliose and fruticose 

 thalli appear in some exotic genera. A plectenchymatous cortex is formed 

 on the thallus of Forssellia, a crustaceous genus from Central Europe, with 

 two species only; the whole thallus is built up of a kind of plectenchyma 

 in some others, but in most of the genera there is no tissue formed. 



The apothecia, as in Ephebaceae, are generally half-closed. 



