184 



CONIFERALES 



features. The occurrence of opposite pits and rims of Sanio in th< 

 younger portion of the xylem is regarded as evidence in support 

 of the view that the stem, while in the main Araucarian, exhibits 

 features indicative of the origin of the Araucarineae from the 

 Abietineae. The presence of .opposite pits in wood in which the 

 normal arrangement is alternate is not surprising if it is admitted 

 that the Coniferous pitting is derived from an earlier scalariform 

 type. Even in stems in which the alternate or opposite pitting 

 is well established it is not very uncommon to find occasional 

 departures from the normal pattern. This Cretaceous stem is 

 one of many generalised types, and the arguments based on the 

 admixture of characters in favour of the greater antiquity of the 

 Abietineae do not present any insuperable difficulty to the opposite 

 view namely that the Araucarineae preceded the other families of 

 the Coniferales. 



Dadoxylon (Araucarioxylon) breveradiatum (Lignier). 



This species from the Cenomanian of Normandy 1 affords one 

 of the few examples of the preservation of phloem, cortex, and pith. 

 Lignier adopted the generic name Arauca- 

 riocaulon: he describes the tracheids as 

 having 1 3 rows of pits, crowded and alter- 

 nate but not flattened. The medullary rays 

 are very short, 1 3 and rarely 4 cells in 

 depth ; there are said to be 8 15 pits in the 

 field (fig. 713). Resiniferous parenchyma is 

 abundant as in the wood referred by Caspary 

 to a special genus Araucariopsis 2 and in 

 Dadoxylon septentrionale Goth. The phloem 

 includes well-preserved sieve-tubes and the 

 cortex is characterised by numerous sclerites, an Araucarian 

 feature. This species appears to be an aberrant type the position 

 of which is by no means clear. 



Among other Cretaceous species are Dadoxylon albianum 3 

 (Fliche) from L'Aube; Dadoxylon Dantzii Pot. 4 from beds pro- 

 bably of Upper Cretaceous age in East Africa, without definite rings 



1 Lignier (07 2 ) p. 290, PL xix. 2 See page 179. 



3 Fliche (97) p 8, figs. 24. 4 Potonie (02) Pis. i., n. 



II 



FIG. 713. Dadoxylon (Ar- 

 aucarioxylon) breveradi- 

 atum. (After Lignier.) 



