s 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 authority of Mr Carruthers is to
be quoted in support of the belief that they are Cryptogamic,
and most nearly allied to the Club-mosses.

[Illustration: Fig. 112.--_Stigmaria ficoides_. Quarter natural
size. Carboniferous.]

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 unmistakable manner.
The _Stigmarioe_ (fig. 112) ordinarily present 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 pit or depression 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 _Stigmarioe_ are
generally found ramifying in the "under-clay," which forms the
floor of a bed of coal, and which represents the ancient soil
upon which the _Sigillarioe_ grew.

[Illustration: Fig. 113.--_Trigonocarpon ovatum_. Coal-measures,
Britain. (After Liudley and Hutton.)]

The _Lepidodendroids and Sigillaroids, though the first were
certainly, and the second possibly, Cryptogamic or flowerless
plants, must have constituted the main mass of the forests of
the Coal period; but we are not without evidence of the existence
at the same time of genuine "trees," in the technical sense of
this term--namely, flowering plants with large woody stems. So
far as is certainly known, all the true trees of the Carboniferous
formation were _Conifers_, allied to the existing Pines and Firs.
They ar