490 CYCADOPHYTA [CH. 



to show that these Indian stems are characterised by certain 

 features, the more compact nature of the secondary xylem and 

 the presence of multiSeriate pitting, which distinguish them from 

 the Cycadeoidea type. Further knowledge of the anatomical 

 features of the WilUamsonia (Bucklandia) stems from other 

 locahties might enable us to recognise these or other peculiarities 

 as constant distinguishing characters of Bucklandia in contrast 

 to the Cycadeoidea stems which bore the Bennettites type of 

 flower. 



Cycadeomyelon. Saporta. 



Casts of the pith-cavity of Cycadean stems, like that shown in 

 fig. 575 projecting beyond the armour of leaf -bases, are occasionally 

 found as separate fossils and cannot always be referred to a 

 particular species of stem. For such detached casts Saporta^ 

 instituted the name Cycadeomyelon: they are characterised by 

 their comparatively large diameter and by the possession of 

 surface-features similar to those on the corresponding cast from 

 a recent Cycadean stem shown in fig. 398, namely spirally disposed, 

 more or less prominent, lozenge-shaped areas formed by the 

 sand or mud filling the cavities left on the decay of the parenchyma 

 of the broad medullary rays of a manoxylic stem. Occasionally 

 a slit at the lower end of a medullary ray area marks the position 

 of the leaf-trace bending outwards from the lower angle of the 

 mesh in the xylem-lattice^. Lignier figures part of a pith-cast 

 of Cycadeomyelon Apperti^ in which each medullary-ray area 

 has a circular depression and not a slit extending from the lower 

 angle: this may indicate that the surface shown on the cast is 

 slightly external to the inner edge of the stele and in a plane where 

 the leaf-traces were embedded in the parenchyma of the rays and 

 free from the xylem-cylinder. 



Large and branched examples of Cycadeomyelon were figured 

 by some of the earlier authors from English Wealden beds 

 as species of Clathraria^ and in many cases these are undoubtedly 

 pith-casts of Bucklandia stems : a similar cast is figured under 



1 Saporta (75) A. p. 331, PI. 119, fig. 3. ^ Lignier (95) p. 11, fig. 1. 



' Ibid. p. 15, fig. 2. 



* Stokes and Webb (24) PI. xLv. ; ManteU (27), etc. See Seward (95) A. pp. 126, 

 130, etc., for other references. 



