126 LYCOPODIALES [CH. 



retain any indications of the cushion-form ; the ridges are the 

 casts of the spaces produced in the cortex by the decay of the 

 sheath of delicate cells surrounding each leaf-trace and by the 

 decay of the thin-walled cells of the parichnos. The occasional 

 forked apex of a ridge is the expression of the fact that the cast 

 was made at the region where the parichnos divides into two arms 

 (cf p. 100). In certain specimens it is possible to connect the 

 Knorria casts with associated lepidodendroid stems which may 

 be determined specifically; but when we have no evidence as to 

 surface-features the fossils may be designated casts of lepido- 

 dendroid stems in the Knorria condition. Such casts are illus- 

 trated by numerous drawings in palaeobotanical literature \ 



b. Bergeria. 



This is another name first used by Sternberg in his classic 

 work, Die Flora der Vorwelt, for casts of lepidodendroid plants 

 such as Steinhauer^ had previously figured as Phytolithiis 

 caiicellatus. Brongniart^ recognised that the application of the 

 generic title Lepidodendron should be extended to include 

 specimens referred by Sternberg to Bergeria, and a few years 

 later Goldenberg* realised that this name does not stand 

 for well-defined generic characters. The correctness of these 

 views was, however, first satisfactorily demonstrated by Car- 

 ruthers^ and by Feistmantel". 



If a Lepidodendron stem loses its superficial layers of outer 

 cortex and in this condition is embedded in sand or mud, the 

 cast is distinguished from that of a perfect stem by the absence 

 of the leaf-scars and by other features. It may, however, still 

 show spirally disposed areas, corresponding approximately to 

 the original leaf-cushions, which are characterised by a small 

 depression or pit either at the apex or near the centre of each 

 oval area: the pit marks the position of the leaf- trace and its 

 parichnos strand. In some cases the exposed surface may be 

 smooth without any indication of leaf-cushions, while narrow 



1 Good examples are given by Sohmalhausen (77) PI. iii. 



2 Steinhauer (18) A. PI. iv. fig. 5. 3 Brongniart (49) A. p. 42. 

 ■> Goldenberg (55). » Carruthers (732) p_ g_ 



" Feistmantel (75) A. 



