128 LYCOPODIALES [CH. 



from the internal and more resistant tissues of the outer cortex, 

 thus producing spaces between each cushion ; further decay 

 would cause rupture of the leaf-traces and the superficial tissues 

 would thus be separated from the rest of the stem. The 

 tendency of Lepidodendron stems to split along the line of 

 phellogen in the outer cortex is seen in fig. 148, A, g. The 

 deposition of sediment on the exposed inner face of this cortical 

 shell would result in the production of a specimen of the 

 Aspidiaria type : the reticulum enclosing the spirally disposed 

 convex areas is formed by the impression of the firmer tissue 

 between the leaf-cushions. 



vi. Lepidodendroid axes known as Ulodendron and Halonia. 

 a. Ulodendron. 



This generic name was suggested by Lindley and Hutton^ 

 for two specimens from the English Coal-measures characterised 

 by leaf-cushions like those of a Lepidodendron, but distinguished 

 by the presence of two vertical rows of large and more or less 

 circular cup-shaped scars. These authors, while recognising 

 the possibility that the fossils might be identical with Lepido- 

 dendron, regarded them as generically distinct. The generic 

 title Ulodendron, though no longer denoting generic rank, is 

 still applied to certain shoots of lycopodiaceous plants which 

 may belong to the genera Lepidodendron, Bothrodendron, and 

 according to some authors ^ also to Sigillaria. 



The large specimen from the Belgian coal-measures, repre- 

 sented in fig. 211, affords a good example of the Ulodendron 

 form of shoot of the genus Bothrodendron, which is described on 

 page 249. The specimen shown in fig. 157 shows the Uloden- 

 dron shoot of Lepidodendron Veltheimianum. 



Casts of large Ulodendron scars are occasionally met with 

 as separate fossils bearing a resemblance to an oval shell. 



In Steinhauer's paper on Fossil Reliquiae^ a drawing is given 



^ Lindley and Button (31) A. Pis. v. and vi. 



■-' Kidston (85). In this important paper Dr Kidston gives a full account of 

 the history of our knowledge of Ulodendron. 

 " Steinhauer (18) A. p. 286, PI. vii. fig. 1. 



