260 COBDAITEAE [CH. 



greater thickness difiers 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^ 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 [Tfj, 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^ 

 as compared with 9 — 12|U,) 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^ that the fossil was not 

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

 from a more southern lofcality. 



Metacordaites. Renault. 



Metacordaites Rigolloti Renault. 



Renault founded this species* and genus on a stem from 

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

 usually attributed to Cordaites. The pith is sohd 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, P]. i. figs. 1—3. 



" Nathorst (11') p. 222. - Renault (96) 



