THE CARBONIFEROUS PERIOD. 



I6 9 



upright in the old Carboniferous swamps, were completely 

 hollowed out by internal decay, till nothing but an exterior 

 shell of bark was left. Often these hollow stumps became 

 ultimately filled up with sediment, sometimes enclosing the 

 remains of galley-worms, land- snails, or Amphibians, which 

 formerly found in the cavity of the trunk a congenial home ; 

 and from the sandstone or shale now filling such trunks some 

 of the most interesting fossils of the Coal-period have been 

 obtained. There is little certainty as to either the leaves or 

 fruits of Sigillaria, and there is equally little certainty as to the 

 true botanical position of these plants. By Principal Dawson 

 they are regarded as being probably flowering plants allied to 

 the existing " false palms" or " Cycads ;" but the high author- 

 ity of Mr Carruthers is to be quoted in support of the belief 

 that they are Cryptogamic, and most nearly allied to the Club- 

 mosses. 



Leaving the botanical position of Sigillaria thus undecided, 

 we find that it is now almost universally conceded that the 

 fossils originally described under the name of Stigmaria are 

 the roots of Sigillaria, the actual connection between the two 

 having been in numerous instances demonstrated in an unmis- 

 takable manner. The Stigmaria (fig. 112) ordinarily present 

 themselves in the form of long, compressed or rounded frag- 



12. Stigma 



Carboniferous. 



ments, the external surface of which is covered with rounded 

 pits or shallow tubercles, each of which has a little pit or de- 

 pression in its centre. From each of these pits there proceeds, 

 in perfect examples, a long cylindrical rootlet ; but in many 

 cases these have altogether disappeared. In their internal 

 structure, Stigmaria exhibits a central pith surrounded by a 

 sheath of scalariform vessels, the whole enclosed in a cellular 

 envelope. The Stigtnarice are generally found ramifying in 



