XXXII] CYCADOXYLON 185 



of a trace. In its passage through the cortex a leaf-trace divides 

 repeatedly, the secondary xylem on the outer face of each strand 

 being retained for a considerable time. 



Our meagre knowledge of the nature of the leaves is based 

 on incomplete fragments found in association with the stem. 

 The leaf is believed to have been simple and characterised by 

 a thick lamina with a hypodermal zone of sclerous strands and 

 several vascular bundles. 



FIG. 452. Stenomyelon tuedianum. Transverse section of stele. 

 (After Kidston; x 7.) 



As Kidston and Gwynne-Vaughan 1 remark, Stenomyelon is a 

 very distinct type; while resembling Sutdiffia in some respects 

 it differs from that genus not only in the structure of the primary 

 stele but in the absence of the system of meristeles which form so 

 characteristic a feature of the latter genus. 



CYCADOXYLEAE. 



Cycadoxylon. Renault. 



This generic term 2 is applied to a few types of Permian and 

 Upper Carboniferous stems possessing a vascular cylinder, which 



1 Kidston and Gwynne-Vaughan (12) p. 269. 



2 Renault (96) A. p. 307. 



