Carboniferous, Europe.]
Externally, the trunks of _Sigillaria_ present strong longitudinal
ridges, with vertical alternating rows of oval leaf-scars indicating
the points where the leaves were originally attached. The trunk
was furnished with a large central pith, a thick outer bark,
and an intermediate woody zone,--composed, according to Dawson,
partly of the disc-bearing fibres so characteristic of Conifers;
but, according to Carruthers, entirely made up of the "scalariform"
vessels characteristic of Cryptogams. The size of the pith was
very great, and the bark seems to have been the most durable
portion of the trunk. Thus we have evidence that in many cases
the stumps and "stools" of _Sigillarioe_, standing 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.
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