102 MEDULLOSEAE [CH. 



Medullosa Leuckarti Goeppert and Stenzel. 



In this species^, also from the Permian of Saxony, the central 

 region including some star-rings is surrounded by sinuous flattened 

 concentric steles (snake-rings) agreeing anatomically with the 

 steles of other species and characterised by the comparatively 

 small breadth of the secondary xylem and phloem (fig. 416, H). 

 Leaf-traces are given off, as in M. anglica and other species, from 

 the outer edge of the primary xylem. In some forms there is 

 a single set of snake-rings ; in others there is a double series. 

 Fig. 418, D, shows part of the secondary xylem of a stele of this 

 species from Chemnitz: the tracheids are in some places con- 

 tinuous with the primary xylem, and on the outer edge of the 

 secondary wood is a cylinder of phloem. A section of Medullosa 

 Leuckarti figured by Goeppert and StenzeP shows some radial 

 rows of very thick-walled elements in the secondary phloem 

 which they describe as bast sclerenchyma, but Solms-Laubach* 

 believes them to be sieve-tubes. Precisely similar elements are 

 figured by Scott* in M. anglica and as this author suggests the thick 

 walls are probably not an original feature. The structure of the 

 primary xylem is more clearly seen in fig. 418, C, and the relation 

 between primary and secondary xylem is shown in fig. 416, I, 

 where the position of the protoxylem may be either exarch or 

 mesarch. The protoxylem is only occasionally recognisable but 

 some of the peripheral primary tracheal groups are undoubtedly 

 mesarch. External to the stele, a part of which is reproduced in 

 fig. 418, D, are strands of stereome elements and beyond them 

 a band of radially elongated cells that may be 'periderm': still 

 farther out there are some imperfectly preserved vascular bundles 

 that are leaf -traces. This species is important as affording a 

 complete demonstration of the organic connexion between the 

 stem and petioles of the Myeloxylon Landrioti type which indicate 

 that the fronds were probably Alethopteroid. 



The specimen on which the diagrammatic drawing reproduced 



1 Goeppert and Stenzel (81) p. 123, PL xvi. figs. 13—15; Solms-Laubaoh (97); 

 Weber and Sterzel (96) B. p. 79, Pis. iv. v. ix. 



2 Goeppert and Stenzel (81) PI. ni. fig. 15. 



3 Solms-Laubaoh (97) p. 179. 

 « Scott (99) p. ,90. 



