XLIV] XENOXYLON 239 



Spitzbergen, as Pinites latiporosus in order to give expression to 

 the combination of distinctive features in both the tracheal and 

 medullary-ray pitting. The most striking characteristics are the 

 very large size of the bordered pits of the tracheids, the occasional 

 (X. phyllocladoides) or constant (X. latiporosum) occurrence of 

 contiguous and vertically flattened and transversely elongated 

 pits on the radial walls, the absence of pits on the transverse and 

 tangential walls of the medullary-ray cells, and the presence of 

 large simple pores on the lateral walls. There is no definite 

 evidence as to the nature of the foliage, though Nathorst 1 has 

 suggested a possible connexion between Elatides and Xenoxylon. 

 Xenoxylon would seem to have been widely distributed in later 

 Jurassic floras. 



Xenoxylon conchylianum Fliche. 



Fliche 2 refers to Xenoxylon a piece of wood from the Muschel- 

 kalk of the Vosges chaiacterised by (i) the occurrence of uniseriate 

 bordered pits compressed above and below and occupying the whole 

 breadth of the tracheids and (ii) a single elliptical pit in the field. 

 The regularity of the pores in the medullary-ray cells and the fact 

 that they are most clearly shown where the preservation is best 

 favour the conclusion that they are an original feature. The 

 medullary rays are usually from 5 to 10 cells in depth. There are 

 no resin-canals and no xylem-parenchyma. Fliche states that the 

 pits on the tracheids are rather less flattened than in X. lati- 

 porosum and they occupy a greater breadth of tracheal wall. The 

 photographs accompanying the description are unfortunately too 

 small to show the important characters. The annual rings are 

 faintly marked and the summer elements are confined to 4 5 rows. 



Despite the resemblance between this Triassic species and those 

 previously described it is by no means certain that Fliche's species 

 is generically identical with the younger types. Large simple 

 pores occur in the medullary-ray cells of recent Conifers belonging 

 to different families, and it is not uncommon to find the bordered 

 pits on the radial walls of tracheids in contact and slightly flattened 

 in wood normally characterised by circular and separate pits. In 



1 Nathorst (97) p. 42. 



2 Fliche (10) p. 232, PI. xxm. figs. 45. 



