SIGILLARIA 223 



section. The existence of this highly differentiated 

 secondary cortex, so distinct from the uniform periderm 

 of 5. Menardi, certainly seems to justify the specific 

 separation of these two forms, even if there were no 

 other diagnostic characters. The fibrous periderm 

 attained an immense development ; fragments 7 or 8 

 cm. thick are found, and these appear to be only 

 exfoliated laminae of a much thicker bark. 



Beyond the secondary cortical zone lies the 

 primary outer cortex, bearing the leaf- bases, where 

 they are preserved. The interest of this species lies 

 chiefly in two points — the transition which it shows 

 between continuous and discrete primary xylem, and 

 the complex character of the secondary cortical 

 zone. 



Both in 5. spinulosa and 5. Menardi the structure 

 of the leaf-bases has been made out, thanks once more 

 to M. Renault's researches. Towards the exterior of 

 the cushion there is a rather thick-walled hypoderma ; 

 the softer tissue within contains the two parichnos- 

 strands already described, and between them lies the 

 vascular bundle (cf. Fig. 92, A). The primary wood 

 forms a narrow transverse band, surrounded by a 

 delicate tissue. 1 The secondary wood is separated by 

 this tissue from the primary xylem ; it forms an arc of 

 radially arranged elements towards the lower side of 

 the bundle. Below this again is a layer of phloem. 

 Some light is thrown on this peculiar arrangement of 

 the parts of the bundle by the structure of the leaf 



1 M. Renault regarded this as primary phloem, which may be correct, as 

 in the leaf the transfusion-tissue (apparently continuous with the secondary 

 xylem) lies outside the primary phloem. See Flore fossile d'Autun et 

 d'£pinac, Part ii. p. 212. 



