XV] LEPIDODENDEON 153 



appearance shown in fig. 168, B, sc ; fig. 169, B and C ; fig, 

 170, B (longitudinal section); fig. 171, D, sc. The compara- 

 tively large clear spaces which characterise this tissue, as seen 

 in fig. 168, B, appear to owe their origin to groups of small 

 cells which gradually break down and give rise to spaces con- 

 taining remnants of the disorganised elements, as in fig. 171, D, 

 and fig. 169, B, b. The secretory tissue seen in fig. 170, B, 

 consists of large and small parenchymatous cells without any of 

 the broad sacs or spaces such as are shown in fig. 169, C. 



Fig. 172 represents a diagrammatic sketch of a transverse 

 section (4 x 3"4 cm. in diameter) of a young shoot from the 

 Lower Coal- Measures of Lancashire figured by Williamson^ in 

 1881 as Lepidodendron Harcourtii. It shows the features 

 characteristic of L. fuliginosum and is of importance as afford- 

 ing an example of a shoot giving off a branch from the stele to 

 supply a lateral axis of the type characteristic of Halonia. The 

 exit of the branch-stele forms a gap in the main stele ; a 

 ramular gap as distinguished from a foliar gap. The outgoing 

 vascular strand is at first crescentic, but becomes gradually 

 converted into a solid stele. The primary xylem of the main 

 stele (black in the figure) consists of a ring six tracheae in 

 breadth ; this is succeeded by a few layers of dark parenchy- 

 matous cells and a band of radially elongated elements, a, which 

 abuts on the secretory zone. The middle lacunar cortex, c^ 

 with Stigmaria rootlets, s, is fairly well preserved. In the outer 

 cortex occur several leaf-traces. It, accompanied by spaces origi- 

 nally occupied by the parichnos strand, p. A band of secondary 

 cortex, consisting chiefly of phelloderm, is seen at pd. The 

 prominent leaf-cushions, some of which show the parichnos, jj, 

 appear to be of the Lepidophloios type. 



It remains to consider the external characters of Lepidoden- 

 droid shoots possessing the anatomical features represented 

 by the comprehensive species Lepidodendron fuliginosum. 



Certain sections exhibiting this type of structure were 

 described by Binney in 1872 as Halonia regularis- on evidence 

 supplied by Mr Dawes, who stated that they were cut from a 



1 Williamson (81) A. PI. lii, p. 288. (Will. Coll. No. 379.) = Binney (72). 



