XLIV] MESEMBRIOXYLON 207 



Phylloclad'oxylon sp. may perhaps be included in Mesembrioxylon 

 though the preservation is hardly sufficiently good to admit of 

 accurate determination. The bordered pits on the tracheids are 

 circular and separate, about 15/x in diameter; the medullary rays 

 have one or rarely two large simple pits in the field. 



Mesembrioxylon woburnense (Stopes). 



An Aptian (Lower Greensand) species from Bedfordshire 

 founded on two blocks of secondary wood and referred to Podo- 

 carpoxylon 1 . The tracheids have 12 rows of bordered pits, the 

 pits in two series being opposite ; Sanio's rims are present. Resin- 

 parenchyma is abundant all through the wood; the medullary 

 rays are for the most part 3 cells deep but vary from 1 to 25 ; there 

 is one large circular or oval pit, or sometimes two, in the field, 

 and a narrow border is occasionally preserved. This species is 

 near to M. Schwendae but there are fewer pits in the field in the 

 English type. 



Mesembrioxylon bedfordense (Stopes). 



This Aptian species 2 is especially characterised by the arrange- 

 ment of the bordered pits on the radial walls of the tracheids ; the 

 pits are uniseriate and occur in chains of 3 10, the border being 

 flattened above and below by contact (fig. 72l,t): the narrower 

 parts of the xylem-elements are often without pits. Xylem- 

 parenchyma is scattered through the wood and the medullary-ray 

 cells have an oval or nearly circular large pit, sometimes with a 

 border (fig. 721, m, p), in the field. The contiguous pits constitute 

 an Araucarian feature though similar pits occur in Cedroxylon and 

 in some other genera. 



Mesembrioxylon Gothani (Stopes). 



Dr Stopes regards this species 3 , from the Aptian of the Isle of 

 Wight, as highly suggestive of the genus Phyllodadus. The 

 medullary rays are generally 2 4 cells deep and there are 1 2 

 large oval simple pits in the field. Xylem-parenchyma is sparsely 

 scattered through the wood, and stone-cells occur in the pith. 



1 Stopes (15) p. 211, PL xx. text-figs. 6063. 



2 Ibid, p. 223, PL xxi. text-fig. 64. 



3 Ibid. p. 228, text-figs. 65, 66. 



