96 STUDIES IN FOSSIL BOTANY 



more important difference is the constant presence, in 

 S. insigne, of continuous medullary rays, which replace 

 the complicated system of vertical and radial parenchy- 

 matous strands in the species above described. In these 

 latter points the Burntisland species differs, not only 

 from 5". plurifoliatum, but from all other species of 

 Sphenophyllum of which the structure is known. For 

 these reasons, and because the older specimens, which 

 have lost their primary cortex, present a very root-like 

 appearance, several palaeobotanists disputed the identi- 

 fication of the fossil as a Sphenophyllum, imagining that 

 it might be a root of a Cycad or of some unknown 

 plant. The discovery of younger plants, still retaining 

 their cortex (Fig. 40) and nodes, and even portions of 

 the leaves, has completely removed these doubts, and 

 justified Williamson's original opinion. 1 The same 

 species has now been found in the Lower Carboniferous 

 of Silesia, of an age comparable to that of the Scotch 

 specimens. In some specimens of Sphenophyllum 

 insigne, the phloem is remarkably well preserved, 

 and large elements, much resembling the sieve-tubes 

 of some recent Cryptogams, are present. 



It is a fact of interest that this, the oldest known 

 Sphenophyllum with structure, presents a less peculiar 

 organisation than the forms from later deposits. This 

 fact would seem to indicate that the remarkable 

 arrangement of the wood-parenchyma in the latter 

 species is a later modification, and not a primitive 

 character of the group. Although the near affinities 



1 Williamson and Scott, I.e. , p. 926. Williamson's original description 

 is in Part v. of his "Organisation of the Fossil Plants of the Coal- 

 measures," Phil. Trans. 1874. 



