190 DAD0XYL0N. 



is not well preserved. It is traversed by a number of parallel 

 veins. It is impossible to refer this fragment to any genus. The 

 closest comparison is with the Gymnosperms, as Mr. Seward has 

 pointed out. 



Casey's Township, Transvaal. Pres. by D. Draper, Esq., 1897. 



Genus DADOXYLON, Endlicher, 1847. 

 (Syuop. Conifer., p. 298.) 



Endlicher defined this genus thus : — " Truncus cylindricus, 

 e medulla centrali, et ligni stratis concentricis obsoletis aut 

 rarius distinctis et e cortice compositus. Vasa (ligni cellulae 

 prosenchymatosae) porosa, poris in series 1-4 spiraliter dispositis, 

 quam maxime appi'oximatis, demum ob mutuant pressionem sex- 

 angularibus, pleTumque nonnisi in parietibus radiis medullaribus 

 parallelis, et invicem oppositis obviis. Radii medullares e cellu- 

 larum parenchymatosarum serie unica v. pluribus formati, simplices 

 v. compositi." 



This genus is now, however, used in a restricted sense, and the 

 following may be regarded as its chief characters: — Petrified wood 

 of Palaeozoic age of the Coniferous type, closely similar to that of 

 the modern Araucariae. Pings of growth usually well marked. 

 Xylem centrifugally developed, tracheides as a rule pitted only 

 on the radial walls. Bordered pits, hexagonal in outline, usually 

 contiguous, pluriseriate, more rarely distant and uni- or biseriate. 

 Pith usually large, fistular or solid. Cortex as a rule without 

 gum-canals or resin-cells, but the latter are sometimes found in the 

 cortex, wood, and pith. 



In both Palaeozoic and Mesozoic rocks petrified woods of the 

 Araucarian type occur, whose precise affinities it is often difficult 

 or impossible to determine. The term Araucarioxylon, Kraus, was 

 at one time ' applied to such specimens, whether of Palaeozoic or 

 Mesozoic age, but it has been recently decided that this name 

 should be restricted to woods of the latter age. 2 The old genus 

 Dadoxylon has been revived, and to it the Palaeozoic specimens are 



1 Schimper (69), vol. ii, p. 380. 



2 Zeiller (00 1 ), p. 280; Knowlton (90), p. 006 ; Scott (02), p. 331. 



