ig6 FORMATION OF COAL. 



been suggested that the stems grow so, which is correct for the 

 elder trees, but when young there [was a pith which gradually 

 became ruptured owing to rapid growth. Next to the pith 

 was a woody zone, composed of wood wedges separated by a 

 prolongation of the pith : these converge at the nodes, and 

 externally appear like furrows extending from one node to another. 

 At the nodes were transverse partitions dividing the stem into 

 divisions. As to the base, it has been contended that the rhizoma 

 converged to a point, the internodes becoming smaller. I have 

 specimens in my collection which have a truncated base, and one 

 with rootlets attached : it is possible, however, that these have 

 been broken near the termination. The latter are most abundant 

 in the Upper Series of the Bristol Coalfield ; but in the Pennant, 

 those with a conical base are mostly met with : in every case, 

 however^ the internodes diminish as they near the base. Calamites 

 were branching plants, but as to the nature of their leaves or 

 whether they bore fruit is considered doubtful. Dr. Dawson 

 considers that they grev/ in muddy flats or perhaps in water ; this, 

 however, is an open question which requires farther research. 

 The Sigillaria and Lepidodendroid plants are now generally 

 supposed to have a close resemblance in their structure, and are 

 classed among the Lycopodiaceae. They consist of a central 

 medullary axis surrounded by other cylinders of barred vessels, 

 a sort of middle bark ; avascular woody cylinder and an outer bark. 

 The vascular woody cylinder seems to have been of a very tough 

 nature, and it is this which has been preserved, the outer bark and 

 inner cylinders having disappeared in the great majority of 

 specimens found. The Sigillaria are very abundant in some seams. 

 They are lirst met with in Devonian rocks, and attain their maximum 

 development during the Carboniferous period, they are unknown 

 in the Permian. The fossil is characterised by longitudinal flutings 

 which divide the wood tissue into ribs. I very much doubt whether 

 these ribs extended through the outer bark 3 from specimens which 

 I have seen underground, and from one in my collection, I am 



