HITHEBTO KNOWN AS STERNBEEGIiE. 345 



allied to Araucaria, exhibiting the structure and arrange- 

 ment of woody fibre and medullary rays, which, according 

 to M. Bj*ongniart, characterise Endlicher's genus Dadoxy- 

 lon. But its pith, instead of being like those of the living 

 Araucariae, belonged to the curious type termed discoid or 

 disciform, resembling those of the recent walnut and white 

 jasmine; whilst the so-called Sternbergias were neither 

 the remains of monocotyledonous stems, nor yet the piths 

 of exogenous plants, but mei^e inorganic casts of central 

 cavities existing within the true piths, which cavities had, 

 under favourable circumstances, become filled with some 

 inorganic material. Though subsequent chemical changes 

 have usually caused either the total disappearance of the 

 vegetable elements, or their conversion into a thin film of 

 carbonaceous matter, these casts of the moniliform cavities 

 have been permanently preserved. 



Fig. 1 represents a portion of the Coalbrookdale fossil 

 split longitudinally, and revealing the different tissues. 

 Even with the naked eye we can distinguish an external 

 bark (a and b\ a middle woody layer (c), and an internal 

 medulla ((/), within which latter tissue is the central cylin- 

 der, representing the so-called Stembergia (h). In order 

 to leave no doubt about the true nature of each of these 

 structures, I have given representations of sections made 

 both horizontally and vertically. Fig. 1 is enlarged to 

 nearly double the size of the original. Fig. 2, which re- 

 presents the extremity of the fragment where it has been 

 broken across, is of the natural size. We see in it the 

 same concentric zones of bark (a and 5), wood (c), and 

 medulla (g), surrounding the central cylinder (A), as in 

 fig. 1. Fig. 3 represents a transverse section of the bark, in- 

 cluding a few fibres of the woody layer, which show that 

 we have reached the innermost portion of the former struc- 

 ture. The external half (3 a) consists of large irregularly 

 formed cells of unequal sizes, and appears to represent the 



2y 



