XLIV] MESEMBRIOXYLON 211 



are represented by Schenk as widely separated and the single pits 

 in the field are narrower and more oblique than in other examples 

 of the genus. The impression made by these species, formerly 

 referred to Phyllocladoxylon and distinguished from one another 

 by no very well-defined characters, is that they agree with certain 

 recent Podocarpineae and with Sciadopitys more closely than with 

 any other recent Conifers; but in the absence of any definite 

 evidence with regard to foliage or reproductive organs it is im- 

 possible to select any one existing genus as the modern representa-- 

 tive of the Arctic and South American fossil species. If the 

 absence of Sanio's rims is accepted as a criterion of affinity, some 

 species of Mesembrioxylon would be included in the list of types 

 aUied to the Araucarineae, but even assuming that the preservation 

 of the wood is such as to admit of their recognition, were they 

 present, their absence does not nullify the evidence afforded by the 

 tracheal and medullary-ray pitting. 



1 Mesembrioxylon Hookeri (Arber) (= Cupressinoxylon Hookeri 

 Arber). 

 A species^ founded on a splendid specimen of silicified wood 

 nearly 9 ft. long and with a diameter of 3 ft. from Tasmania 

 exhibited in the Geological Department of the British Museum. 

 The stem was discovered early in the nineteenth century in Ter- 

 tiary basaltic lava on the Macquarie plains. Dr Arber quotes 

 Sir Joseph Hooker who gives an interesting account of the method 

 of preservation of the decorticated wood. The annual rings are 

 well marked and narrow ; the tracheids have usually a single row 

 of circular and scattered bordered pits on their radial walls and 

 smaller pits are abundant on the tangential walls. Sanio's rims 

 are clearly shown on some of the tracheids. The medullary rays 

 are generally uniseriate and in exceptional cases reach a depth of 

 over 20 cells. Arber speaks of the occurrence of a small simple 

 pit on the radial wall of the ray cells ; an examination of the sec- 

 tions in the British Museum showed that for the most part the 

 pitting on the ray cells is not preserved but in some places a single, 

 fairly large, simple pit occurs in the field. Resin-parenchyma is 

 present in both spring- and summer- wood. 



1 Arber (04). 



14—2 



