CH. XXXIII] POROXYLON 215 



The slender cylindrical stems, not exceeding 2 — 3 cm. in 

 diameter in specimens so far recorded, bore large broadly linear 

 leaves similar in form and venation to those of some species of 

 Cordaites which were attached singly to slightly swollen nodes 

 separated from one another by internodes several centimetres 

 long. The base of the rather fleshy lamina passes imperceptibly 

 from the narrow lower portion into a tangentially expanded 

 petiole which forms a decurrent ridge on the stem. Axillary 

 buds frequently occur. Little is known of the leaf-impressions, 

 but if Grand'Euryi is correct in his identification of certain speci- 

 mens from French Stephanian beds as the leaves of Poroxylon, 

 the lamina reached a length of 1 met. and a breadth of 15 — 20 cm. 

 In habit the stems probably resembled some of the larger-leaved 

 Bamboos. The only evidence bearing on the nature of the re- 

 productive organs is furnished by Grand'Eury who believes that 

 some Rhabdocarpus seeds and bractless inflorescences associated 

 with the leaves assigned to Poroxylon belong to that genus. 



The single cylindrical stele has a relatively large sohd pith, 

 the perimeduUary region being characterised by the occurrence 

 of a row of primary crescentic strands of centripetal xylem of 

 exarch type, though not improbably in some cases shghtly mesarch, 

 varying in size and shape and forming single or paired bundles. 

 These strands represent the xylem of collateral leaf-traces similar 

 to those of Lyginopteris but differing in the absence of weU- 

 defined centrifugal elements: the curved form of some of the 

 xylem strands gives them an appearance similar to that of 

 the leaf-traces of Lyginopteris. The leaf-traces, except in the 

 lower part of their course through the pith, are double and pass 

 through several internodes before the centripetal tracheids die 

 out. The secondary xylem (fig. 463) is manoxylic and very similar 

 to that of Lyginofteris though rather less parenchymatous. The 

 secondary phloem and cambium are often very well preserved. 

 No endodermis and no distinct pericycle has been recognised. 

 The cortex is parenchymatous and, like the pith and to some 

 extent the phloem, contains numerous secretory sacs; in the 

 outer cortex the presence of hypodermal strands is a prominent 



1 Grand'Eury (05). 



