2 THE DETEBMIKATI02S OF LICHE>^S 1^ THE TIELD 



KEY TO THE GENEKA OF BKITISH LICHENS. 



Typical specimens are referred to : abnormal plants cannot always be placed 

 in their proper genera by means of the key. 



Th. of leaf -like bodies or sqnamules ± horizontally 



placed A. 



Th. of filaments or cylinders, or of ifcerect and 



strap-shaped bodies (lacinite) B. 



Th. a granular, tartareous or powdery crust, or 



wanting C. 



A. Thallus foliose oe squamulose. 



1. Ap. borne on erect elevated cups, or on 



cylindrical bodies (podetia) 2. 



Thecia borne on the thallus or absent 3. 



2. Podetia solid, with minute squamules crowded 



on them. Spores septate Stereocaulon. 



Podetia hollow, usuall}^ without squamules. 



Spores simple Cladonia (a) *. 



3. Th. of large lobes, not less than 4 mm. broad, 



and often much broader 4 (J). 



Th. of small or minute lobes 23. 



4. Th. gelatinous when moist, with blue-green 



algie {Nostoc) distributed in it 5. 



Th. not gelatinous when moist, the algal 



cells forming a dehnite la^'er beneath the 



upper surface 6. 



'). Th. with a cellular cortex. Sp. muriform (c). Leptogium (r/). 

 Th. thickish, not cellular. Sp. muriform ... Collema (14-15). 

 Th, thin or flaccid, not cellular except in or 



near the ap. Sp. elongate-fusiform with 3- 



many transverse septa (>S'. nigrescens and 



S.flaccidiis) SynechoWastus. 



6. Th. greyish when dr}^ usu. umbilicate (<?), 



and with perithecia dotted on the uj^per 



surface (Z). miniatum and D. aquaticiini). Dermatocarpon. 

 Th. blackish when dr}^, usu, umbilicate. 



Ap, without a thalline margin, the disc 



twisted or plaited (gyrose ) 7. 



Th. not umbilicate. Ap, usu, with a thalline 



margin, the disc not gyrose 8. 



7. Th. pustulate (/'). Aj), with 2:>lane disc, 



Sp, 1 , dark, muriform Umbilicaria. 



Th, not or little pustulate, Ap. usu, with 



gyrose disc, Sp, 8, colourless, simple Gyrophora, 



8. Th, with whitish or yellowish depressions 



(cyphellae) or spots {c/) (pseudoc^^phellse) 

 beneath. Ap, with thalline margin, Sp. 1- 



3 septate 9, 



Th, without cyphellse or pseudocyphellse 



beneath 10. 



^ The notes are to be found at the ends of the Sectional Keys A. B, <fec. 



