174 LYCOPODIALES [CH. 



them on the living tree. Fig. 185, B, illustrates the appearance of 

 a stem in a partially decorticated condition (Bergeria state). 

 A further degree of decortication is seen in fig. 185, A, which 

 represents the Knorria condition. 



Fig. 157 shows a Ulodendron axis of this species; in the 

 lower part the specimen illustrates the partial obliteration of 

 the surface features as the result of the splitting of the 

 outer bark consequent on growth in thickness of the tree. 

 By an extension of the cracks, shown in an early stage in 

 fig. 157, the leaf-cushions would be entirely destroyed and the 

 surface of the bark would be characterised by longitudinal 

 fissures simulating the vertical grooves and ridges of a Sigil- 

 larian stem. The large stumps of trees shown in the frontis- 

 piece to Volume I. are probably, as Kidston^ suggests, trunks 

 of L. Veltheimianum in which the leaf-cushions have been 

 replaced by irregular longitudinal fissures. In old stems of 

 Sigillaria the enlarged parichnos areas constitute a characteristic 

 feature (p. 205), but it does not follow that the absence of large 

 parichnos scars is a distinguishing feature of all Lepidodendra. 



In this species, as in others, the form of the leaf-cushion 

 exhibits a considerable range of variation dependent on the 

 thickness of the shoot ; the contiguous cushions of young 

 branches become stretched apart as the result of increasing 

 girth of the whole organ, and casts of still older branches may 

 exhibit very different surface-features^. The leaves as seen 

 on impressions of slender branches are comparatively short, 

 reaching a length of 1 — 2 cm. It is important to notice that 

 leafy twigs of this species may bear terminal cones ^ resembling 

 in form those of Picea excelsa and other recent conifers, though 

 differing essentially in their morphological features. 



The fossil stumps of trees represented in the frontispiece to 

 Volume I. bear horizontally spreading and dichotomously 

 branched root-like organs having the characters of Stigmaria 

 ficoides*. Geinitz has suggested that Stigmaria inaegualis 

 Gopp. may be the underground portion of Lepidodendron Velthei- 

 mianum. 



1 Young and Kidston (88) A. 2 Potonie (012) gg. 72, p. 117. 



3 Stur (75) II. A. PI. XXXVI. fig. 9. * See Chap. xvii. 



