258 COEDAITEAE [CH. 



rays 1 27 cells in depth; the tracheids have usually two or 

 sometimes three rows of alternate and contiguous bordered pits 

 on the radial walls. Arber regards the absence of a discoid pith 

 as a fatal objection to a reference of the stems to Cordaites and 

 speaks of them as affording further evidence of the occurrence 

 of Coniferae in the higher Coal Measures of the Midlands. It is, 

 however, impossible to determine the position of the species in 

 the absence of any data with regard to the structure of the peri- 

 medullary region, and without such information we are hardly 

 justified in regarding Dadoxylon Kayi as a member of the Coni- 

 ferales. 



Dadoxylon Pedroi Zeiller. 



This species from Upper Carboniferous or possibly Lower 

 Permian strata in Brazil 1 has a pith 3-8 cm. in diameter composed 

 of parenchyma with scattered secretory sacs and characterised 

 by the occurrence of three equidistant bays projecting into the 

 cylinder of wood (fig. 476, A) which extend through the length 

 of the specimen (6 cm.) : these, as Zeiller suggests, may be con- 

 nected with the departure of leaf -traces or branches. The xylem 

 is entirely composed of centrifugal elements and shows a broad 

 transitional zone (fig. 476, B) including spiral, scalariform, and 

 reticulate tracheids, but the bordered pits are less numerous and 

 less crowded than in many species of Dadoxylon. The rays are 

 1 2 cells broad and reach a depth of 50 cells. The most striking 

 features are the solid and not discoid pith with its three rounded 

 bays and secretory canals, also the smaller number and frequently 

 circular form of the pits on the tracheids. Zeiller considers that 

 the stem is that of some Cordaitean plant though probably not 

 a true Cordaites. White 2 questions the advisability of adopting 

 the generic name Dadoxylon and suggests the possibility, though 

 without any satisfactory evidence, that it is the stem of a Ganga- 

 mopteris. Failing further information, there would seem to be 

 no sufficient reason for the institution of a distinctive generic 

 name. 



1 Zeiller (95) B. p. 619, PL ix. figs. 819. 



2 White (08) B. p. 577. 



