i 3 2 STUDIES IN FOSSIL BOTANY 



tion of various Lepidodendra. Thus, when the epidermis 

 had been lost before fossilisation, some of the character- 

 istic markings disappear, or change their form, and we 

 get the so-called genus Bergeria. If the destruction had 

 gone a little deeper, removing the outer layers of cortex, 

 the leaf-trace is the only print that remains, and that now 

 lies in the middle of each rhombic area, giving rise to the 

 form called Aspidiaria. Lastly, where the whole bark 

 of an old stem had been stripped off, a totally different 

 appearance is produced, resembling an irregularly fluted 

 column. The inclined, overlapping ridges here corre- 

 spond to the course of the leaf-trace bundles through 

 the middle cortex, and on this state of preservation 

 the genus Knorria has, in part at least, been founded. 1 

 Leaving these false genera, which are only of botani- 

 cal interest in so far as they illustrate the difficulties of 

 the subject, we pass on to a group of fossils which are 

 really distinct from, though closely allied to, Lepido- 

 dendron. This is the genus Lepidophloios, typically 

 characterised by the form of the scale-like, imbricating 

 leaf-cushions, which are in most cases transversely elon- 

 gated, the horizontal diameter exceeding the vertical 2 

 (Fig. 62, p. 156). The leaf-scar, which bears the usual 

 three prints, is also, as a rule, elongated in the horizontal 

 direction, and of rhomboidal or oval form. Another 

 peculiarity is, that in Lepidophloios the leaf-cushions are 

 very prominent, with the pyramidal form much more 

 marked than in Lepidodendron (see Fig. 68, B, p. 169). 

 It appears that the leaf-scar was placed towards the 



1 Illustrations of these forms of preservation will be found in Solms- 

 Laubach's Fossil Botany, English edition, Figs. 19 and 20. 



2 See Kidston, "On the British Species of the Genus Lepidophloios,'' 

 Trans. Roy. Soc. Edinburgh, vol. xxxvii. 1893. 



