334 SYSTEMATIC 



Thallus of small fruticose fronds. 



Gonidia occupying the central strand 4. *Lichinodium Nyl. 



Gonidia not in the centre. 



Apothecia immersed 5. Lichina Ag. 



Apothecia superficial. 



Paraphyses present 6. *Lichinella Nyl. 



Paraphyses absent 7. *Homopsella Nyl. 



XXXIX. CoLLEMACEAF. 



The most important family of the gelatinous lichens and the most 

 numerous. Collema is historically interesting as having first suggested the 

 composite thallus. Algal cells, Nostoc, which retain the chain-like form 

 except in Leprocollenia, a doubtful member of the family. The thallus varies 

 from indeterminate crusts to lobes of considerable size ; occasionally the 

 lobes are narrow and erect, forming minute fruticose structures. In the 

 more primitive genera the thallus is non-corticate, but in the more evolved, 

 the apical cells of the hyphae coalesce to form a continuous cellular cortex, 

 one or more cells thick, well marked in some species, in others rudimentary; 

 the formation of plectenchyma also occurs occasionally in the apothecial 

 tissues of some non-corticate species. 



The apothecia are superficial except in Pyrenocollema, a monotypic genus 

 of unknown locality. They are generally lecanorine, with gonidia entering 

 into the formation of the apothecium : in some genera they are lecideine or 

 biatorine, being formed of hyphae alone. The spores are colourless and vary 

 in form, size and septation. 



Apothecia immersed ; spores fusiform, i-septate I. *Pyrenocollema Reinke. 



Apothecia superficial. 

 Thallus without a cortex. 



Spores simple, globose or ellipsoid. 



Thallus crustaceous 2. *Leprocollema Wain. 



Thallus largely squamulose-fruticose. 



Apothecia lecideine (dark-coloured) 3. *Leciophysma Th. Fr. 



Apothecia lecanorine 4. Physma Massal. 



Spores variously septate or muriform. 



Apothecia biatorine (light-coloured) 5. *Homothecium Mont. 



Apothecia lecanorine 6. Collema Wiyg. 



Thallus with cortex of plectenchyma. 

 Spores simple. 



Spores globose 7. Lemmopsis A. Zahlbr. 



Spores ellipsoid, with thick subverrucose wall... 8. *Dichodium Nyl. 



Spores vermiform, spirally curved 9. *Koerberia Massal. 



v Spores variously septate or muriform. 



Apothecia biatorine (light-coloured) 10. *Arctomia Th. Fr. 



Apothecia lecanorine II. Leptogium S. . Gray. 



