XXX] STELOXYLON 165 



of the leaves by compact branches of the stelar network instead 

 of the bundles detached as leaf-traces from a stem-stele of 

 Medullosa (the origin of a leaf-trace in Steloxylon is shown in 

 fig. 441,, C) ; (iii) the absence of a peripheral system of vascular 

 plate-rings and the irregular distribution of cylindrical and plate- 

 steles in the ground-tissue. Nothing is known of the reproductive 

 organs or leaves beyond the structure of the attached leaf -bases. 

 The opinion expressed by P. Bertrand 1 that the fossil described 

 by Stenzel as Asterochlaena (Clepsydropsis) kirgisica is the petiole 

 of Steloxylon was abandoned after the additional facts published 

 by Solms-Laubach. 



As regards the affinities of Steloxylon : the structure of the 

 steles agrees closely with that of the star- and plate-rings of a 

 Medullosa, while the pitting of the tracheids is more like that in 

 Medullosa than Cladoxylon. In the tendency to a more radial 

 than tangential disposition of the band-like steles Steloxylon 

 recalls Cladoxylon rather than Medullosa, but in Cladoxylon the 

 vascular system does not form an irregular network as in Steloxylon. 

 The information as to the structure of the primary xylem is very 

 meagre, but it points to a closer connexion with Medullosa than 

 with Cladoxylon. On the whole Steloxylon may perhaps be 

 defined as a genus allied to the Medulloseae in the anatomical 

 features of the stem more closely than to other genera, but suffi- 

 ciently distinct to be excluded from the Medulloseae as at present 

 understood 2 . 



1 P. Bertrand (08); (11) p. 47 (footnote). 



2 In a recent note on Steloxylon to which Dr Scott has drawn my attention 

 Bertrand records the genus from Saalfeld (Upper Devonian) and expresses the 

 opinion that Steloxylon may be a condition of Cladoxylon and not a distinct type 

 P. Bertrand (14) p. 448. 



