96 MEDULLOSEAE [CH. 



they appear to be without secondary tracheids as in M. pusilla. 

 A zone of secondary cortex encloses the vascular system as in the 

 other British stems: it is pointed out by Miss de Fraine 1 that 

 this tissue, usually described as a deep-seated periderm, must 

 have differed from cork in that there is no sign of drying up or 

 decay in the tissues external to it. The leaf-bases are of the usual 

 Myeloxylon type. In size this species is intermediate between 

 Medullosa anglica and M. pusilla. 



FIG. 417. Medullosa centrofilis. Transverse section showing the deep-seated 

 'periderm' (broken line) surrounding four steles. (After de Fraine.) 



Medullosa stellata Cotta. 



Gotta 2 described Medullosa stellata as a stem characterised 

 by the occurrence of several many-rayed stellate columns ('viel- 

 strahlige Sternsaule') in a pith enclosed by a double cylinder of 

 secondary xylem. The so-called pith is the central ground-tissue 

 of the stem and the double ' striated ring ' of Cotta is a cylindrical 

 stele identical in structure with each of the steles of Medullosa 

 anglica but having a tubular form instead of forming a relatively 

 broad and short band (cf. fig. 416, D and A). Goeppert 3 in his 

 Permian Flora gave a detailed account of the species, some of 

 his sections being cut from Cotta's material, and by the employ- 

 ment of varietal epithets emphasised the range of variation 

 within the limits of the type. Goeppert and Stenzel 4 and, several 



1 De Fiaine (14) p. 259. See also Kisch (13). 



2 Cotta (32) B. p. 66, PI. xm. The well-preserved specimen figured by Cotta 

 in his PL xin. fig. 2 is in the Dresden Museum. 



3 Goeppert (65) A. p. 209, Pis. XL. XLm. 



4 Goeppert and Stenzel (81). 



