XLIV] CLASSIFICATION OF CONIFEEOTTS WOOD 173 



II. CUPRESSINOXYLON. (Including Glyptostrohoxyhn and 

 Taxodioxylon.) 

 , Xylem-parenchyma scattered through the wood and not con- 

 fined to any particular region, often containing resin; the trans- 

 verse walls may be thick and pitted. Medullary rays uniseriate, 

 horizontal and tangential walls smooth (unpitted) ; there are 

 generally several small pits in the field though in some species 

 referred to this genus there may be a single pit. In the region 

 of the spring-wood the pore of the apparently bordered ray-pits 

 is more or less horizontal ; but the form and position of the pore 

 are variable. 



Resin-canals absent except in wounded parts of the wood. 

 Jurassic to Recent. 



III. TAXOXYLON. 



The same anatomical features as in Cwpressinoxylon except 

 that the tracheids of the secondary xylem have spiral thickening 

 bands. Tertiary to Recent. 



IV. MESEMBRIOXYLON. Gen. nov. (Including Podocar- 



■poxylon, Phyllodadoxylon and Paraphyllocladoxylon.) 

 Xylem-parenchyma usually present and scattered, but it is 

 not so characteristic a feature as in Cupressinoxylon. 



Medullary rays usually uniseriate; the pitting is confined to 

 the radial walls as in Cupressinoxylon but in the region of the spring- 

 wood the pore is obhque or more or less vertical ; in the summer- 

 wood the pits in the field are indistinguishable from those of 

 Cupressinoxylon. There are often several pits in the field but in 

 some species there may be one or two large simple pits in the field. 

 Resin-canals present only in wounded parts of the wood. 

 Jurassic to Recent. 



V. PARACEDROXYLON. 



A genus of doubtful afiinity. Bordered pits on the tracheids 

 usually separate ; no rims of Sanio. 



Xylem-parenchyma confined to wounded regions. Medullary- 

 ray cells pitted only on the radial walls except in the injured parts 

 of the wood where the other walls may be pitted. There are 4—6 

 circular, apparently bordered, pits with an oblique pore in the 



