260 CORDAITEAE [CH. 



greater thickness differs from that of Cordaites leaves. Renault 

 speaks of the rays as a cycadean feature, but they are only two 

 cells in width and shorter than in recent Cycads. 



Dadoxylon spetsbergense Gothan. 



In this species 1 from Spitzbergen, of doubtful age though 

 probably Palaeozoic, there is no xylem-parenchyma and the 

 medullary rays are from 2 to 5 cells deep; the bordered pits 

 occur in 1 2 or rarely 3 rows on the radial walls of the tracheids ; 

 they are alternate but not flattened and characterised by their 

 small size (7/z, high); they do not cover the whole face of the 

 tracheids. It is pointed out that in many Palaeozoic and Mesozoic 

 Dadoxylons the pits are larger than in recent species (16 17-5/z 

 as compared with 9 12/x) while in D. spetsbergense they are still 

 smaller. The large size of the medullary-ray cells is another 

 noteworthy feature, also the absence of annual rings, a character 

 possibly connected with conditions of growth in northern regions. 

 It is, however, pointed out by Nathorst 2 that the fossil was not 

 found in situ and, as he says, it may have been carried by currents 

 from a more southern locality. 



Metacordaites. Eenault. 

 Metacordaites Rigolloti Renault. 



Renault founded this species 3 and genus on a stem from 

 Autun which, like D. Pedroi, differs in certain respects from stems 

 usually attributed to Cordaites. The pith is solid and contains 

 secretory ducts and cells; the tracheids have often a single row 

 of pits, and multiseriate pitting is much less common than in 

 Dadoxylon. The medullary rays are generally 1 6 cells deep. 

 A striking feature is the occurrence of groups of five vascular 

 bundles penetrating the secondary wood in V-shaped groups, 

 each group being regarded as a multiple leaf-trace, a type recently 

 recognised by Thomson in D. Brandlingii. In one of Renault's 

 figures a larger scar, presumably a branch-scar, is shown imme- 

 diately above a group of foliar bundles. The genus Metacordaites 

 is considered by its author to be intermediate between Conifers 



1 Gothan (10) p. 5, PI. i. figs. 13. 



2 Nathorst (II 3 ) p. 222. 3 Renault (96) 



