XV] LEPIDODENDRON 139 



Halonia ; he regards it as a Ulodendron branch of Sigillaria 

 discophora (Konig). Until specimens with more clearly pre- 

 served external features are forthcoming it is impossible to 

 settle the point in dispute, but on the facts before us there 

 would seem to be a prima facie case in favour of Weiss's 

 contention. 



The designation Halonia may be retained as a descriptive 

 term for Lepidodendroid shoots characterised by spirally dis- 

 posed scars or tubercles and bearing leaf-cushions of the Lepi- 

 dophloios tjrpe. In the case of specimens showing prominent 

 tubercles, the superficial tissues are usually absent and, as in 

 the fossil represented in fig. 161, the name Halonia does not 

 necessarily imply the presence of leaf-cushions of a particular 

 type. 



vii. Anatomical characters of Vegetative Lepidodendron shoots 

 (Lepidodendron and Lepidophloios). 



The type already described under the name Lepidodendron 

 vasculare differs from those dealt with in the following pages 

 chiefly in the anatomy of the stele. The simplest and probably 

 most primitive type of Lepidodendron stem is that in which 

 the xylem forms a solid rod ; the, type of stele most frequently 

 represented is that of L. Harcourtii, L. fuliginosum, and other 

 species in which the diameter of the stele is greater and a 

 cylinder of primary xylem encloses a comparatively large 

 parenchymatous pith. 



1. Lepidodendron esnostense, Renault ^ 



This species was founded by Renault on petrified specimens 

 from the Culm beds of Esnost in France. The surface of a 

 young twig bears prominent leaf-cushions of elongated rhom- 

 boidal form similar to those of Lepidodendron ohovatum 

 (fig. 173) and other species. In older branches the primary 

 cortex is replaced by a considerable thickness of radially dis- 

 posed secondary cortical tissue which, as shown in tangential 

 section, consists of a reticulum of elongated pointed elements 



1 Renault (96) A. p. 175, Pis. xxxiii. xxxiv. 



