23 



in some other Coniferous trees, the pith increased in size 

 with the growth of the stem or branch. There are, how- 

 ever, Sternbergiae which have not belonged to Dadoxylon. 

 I have figured 1 specimens which show, attached to them, 

 multiporous tissue like that of Poroxylon or Dictyoxylon. 

 Others are enveloped with scalariform tissue like that of 

 Lepidodendron or Lepidofloios. This fact was long ago ob- 

 served by Corda. Others show pseudo-scalar! form and 

 discigerous tissue like those of Cordaites, or of the peculiar 

 type of supposed Sigillaroid trees above referred to. Thus 

 it is apparent that the Sternbergia piths belonged to a num- 

 ber of trees ranging from Gymnosperms of high type to 

 Acrogens. I may remark here that the true Calamodendra, 

 of which Calamites approximates is a type, in so far as the 

 medullary cylinder is concerned, are really internal casts of 

 pith cavities, originally surrounded by a thick woody en- 

 velope showing psuedo-scalariform and discigerous tissue, 

 and, therefore, not very dissimilar from that of Cordaites. 

 Williamson has shown, however, that the medullary rays 

 and other structures were diiferent, and the stems of 

 Calamodendra were jointed in relation to the support of 

 whorls of organs. If these Calamodendra were really 

 Acrogens allied to Catamites, they present the same curious 

 resemblance to Gymnosperms which we see in another form 

 in one of the types of Sigillaria, and warn us that the 

 structures of stems and the character of fructification may 

 not have been correlated in the Carboniferous in the same 

 manner as in modern stems. 



Doubts of this kind are further justified by the considera- 

 tion of the stems known as Poroxylon, Medullosa, Cycadeo- 

 xylon, Colpoxylon, Lyginodendron, Kaloxylon and Heterangiwn, 

 several of which have recently been described in great 

 detail by Williamson and by Renault These have a true 

 medulla, surrounded by a cylinder of discigerous or reticu- 

 lated tissue, arranged radially and traversed by medullary 

 rays. Such characteristics would well suit a gymnosper- 



1 Journal Geol. Society, 1871. 



