460 PAL.EOBOTANY. 



pith is surrounded by a woody cylinder, consisting of ligne- 

 ous wedges, composed of punctated (discigerous) and scalari- 

 form vessels, and separated by medullary rays. Outside the 

 woody axis is an inner bark composed of long durable fibres 

 of " bast-tissue," the whole surrounded by a thick outer bark 

 of dense cellular tissue. " The trunk when old lost its regular 

 ribs and scars, owing to expansion, and became furrowed like 

 that of an Exogenous tree." The roots, as will be seen im- 

 mediately, constitute the fossils known as Stifjmaria. The 

 leaves are believed to be the so-called Cyjjcritcs, long, narrow, 

 rigid, and two- or three- nerved. The fruits are supposed to 

 be TrigonocmjKi, " borne in racemes on the upper part of the 

 stem." Upon the whole, Dr Dawson is disposed to adopt 

 the view, originally put forth by Brongniart, that the Sigil- 

 laricv find their nearest living allies in the Cycads and that 

 if not actually referable to the Gymnospermous Exogens, 

 tliey may be intermediate between these and the higher 

 Acrogens. 



Mr Carruthers, on the other hand, describes Sigillaria as 

 consisting of a central cellular pith or medulla, surrounded 

 by a sheath consisting wholly of scalariform vessels, the whole 

 enveloped in an external cortical mass of cellular tissue. 

 The medullary sheath is perforated by meshes for the pas- 

 sage outwards of the vascular bundles which go to the axial 

 appendages (the leaves and branches) ; but there are no true 

 medullary rays. Upon these grounds, Mr Carruthers decides 

 against the view that Sigillaria is a Gymnospermous Exogen, 

 and he regards it as Cryptogamic and Lycopodiaceous. He 

 also discredits the assertion that discigerous tissue is present, 

 and describes the fruit as consisting of cones or strobiles. 



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 un- 

 mistakable manner. The Sligmarim (fig. 710) ordinarily pre- 

 sent themselves in the form of long, compressed or rounded 

 fragments, the external surface of which is covered with 

 rounded pits or shallow tubercles, each of which has a little 



