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 fa-mily of the gelatinous Hchens 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 Leprocollema, 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 corte-x. 



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 Wigg. 



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 g. *Koerberia Massal. 



Spores variously septate or muriform. 



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



Apothecia lecanorine 11. Leptogium S. F. Gray. 



