xv] 



I.EPIDODENDRON 



99 



Sigillaria, but as the leaves of these two genera are constructed 

 on the same plan the identification is of secondary importance. 

 The single xylem bundle consists of primary tracheae only, at 

 least in such laminae as have been identified as Lepidodendroid, 

 Surrounding the xylem strand occur delicate parenchymatous 

 cells in some cases accompanied by darker and thicker-walled 

 elements. As in Sigillaria, the leaves of which are more fully 

 described on page 210, a fairly broad sheath of wider and shorter 

 scalariform or spiral transfusion tracheids surrounds the con- 



B 



Fig. 143. A. Stomata in surface- view (Lepidodendronl). a, parenchyma; 

 t, transfusion tracheae; x, xylem. (Manchester University 

 Collection E. 723). 

 B, C. Lepidodendron esnostense Ren. (After Renault.) 



ducting strand (figs. 142, t; 143, B, C, t). As Kenault shows in the 

 case of Lepidodendron esnostense^, the small leaves of which are 

 1-5 — 2 mm. broad at the base and several centimetres long, the 

 stomatal grooves and keel die out towards the apex when the 

 lamina assumes a more nearly circular form (fig. 143, C). 



The area of the cushion excluding the leaf-scar is spoken of 

 by some writers as the field. Below the leaf-scar the kite- 

 shaped cushion tapers to a gradually narrowing basal position: 

 in Lepidodendron Veltheimianum, a species characteristic of 



1 Renault (96) A. Pis. xxxiii. xxxiv. p. 178. For a good section of another 

 Lepidodendron leaf, see Scott (08) p. 160, figs. 64, 65. 



