STRUCTURES PECULIAR TO LICHENS 135 



B. Classification 

 Forssell has drawn up a classification of these structures, as follows : 



I. Cephalodia vera. 



1. Cephalodia epigena (including perigena) developed on the upper 

 outer surface of the thallus, which are tuberculose, lobulate, clavate or 

 branched in form. These are generally corticate structures. 



2. Cephalodia hypogena which are developed on the under surface 

 of the thallus; they are termed "thalloid" if they are entirely superficial, 

 and " immersed " when they are enclosed within the tissues. They are non- 

 corticate though surrounded by a weft of hyphae. Forssell further includes 

 here certain placodioid (lobate), granuliform and fruticose forms which 

 develop on the hypothallus of the lichen, and gradually push their way up 

 either through the host thallus, or, as in Lecidea panaeola, between the thalline 

 granules. 



Nylander^ arranged the cephalodia known to him in three groups: 

 (i) Ceph. epigena, (2) Ceph. hypogena and (3) Ceph. endogena. Schneider^ 

 still more simply and practically describes them as Ectotrophic (external), 

 and Endotrophic (internal). 



II. PSEUDOCEPHALODIA. 



These are a small and doubtful group of cephalodia which are apparently 

 in very slight connection with the host thallus, and show a tendency to 

 independent growth. They occur as small scales on Solorina bispora^ and 

 .S. spongiosa and also on Lecidea pallida. Forssell has suggested that the 

 cephalodia of Psoroma hypnorum and oi Lecidea panaeola might also be in- 

 cluded under this head. 



Forssell and others have found and described cephalodia in the following 

 families and genera: 



Sphaerophoraceae. 



Sphaerophorus {S. stereocauloides). 



Lecideaceae. 



Lecidea {L. panaeola, L. consentiens, L.pelobotrya, etc.). 



Cladoniaceae. 



Stereocaulon, Pilophorus and Argopsis. 



Pannariaceae. 



Psoroma (P. hypnorum). 



Peltigeraceae. 



Peltigera {Peltidea), Nephroma and Solorina. 



^ Nylander 1878. ^ Schneider 1897. ^ jjue 1910. 



