20 



but this is radially arranged, with the individual cells 

 quadrangular in cross-section. The cross-bars are similar 

 on all the sides, and usually simple and straight, but some- 

 times branching or slightly reticulated. The wall inter- 

 vening between the bars has extremely delicate longitudi- 

 nal waving lines of ligneous lining, in the manner first de- 

 scribed by Williamson, 1 as occurring in the scalariforn tissue 

 of certain Lepidodendra. (Fig. 4.) A few small radiating 

 spaces, partially occupied with pyrites, obscurely represent 

 the medullary rays, which must have been very feebly 

 developed. The radiating bundles passing to the leaves run 

 nearly horizontally ; but their structure is very imperfectly 

 preserved. The stem being old and probably long deprived 

 of its leaves, they may have been partially disorganized 

 before it was fossilized. The outer surface of the axis is 

 striated longitudinally, and in some places marked with 

 impressions of tortuous fibres, apparently those of the 

 inner bark. In the cross-section, where weathered, it shows 

 concentric rings ; but under the microscope these appear 

 rather as bands of compressed tissue than as proper lines of 

 growth. They are about twenty in number. Though 

 apparently of very lax tissue, the wood of the outer cylinder 

 may, in consequence of the strength of the vertical rods and 

 transverse bars of ligneous lining, have been of considerable 

 firmness, which would indeed seem to have been implied in 

 the manner of its preservation within the hollow bark." 



This stem is evidently that of a Sigillaria of the Diploxylon 

 type, with a slender woody axis wholly of scalariform 

 tissue and a thick inner bark, probably mostly of cellular 

 tissue of a lax and easily decomposed character, but pro- 

 bably also with bundles of fibres. This was protected and 

 strengthened externally by an outer bark of sclerenchy- 

 matous cells, now converted into coal. 



1 Monthly Microscopical Journal, August, 1860. 



