connection with some other
well-known plant or tree. It was noticed that above the coal, in the
roof, stigmariae were absent, and that the stems of trees which occurred
there, had become flattened by the weight of the overlying strata. The
stigmariae on the other hand, abounded in the _underclay_, as it is
called, and were not in any way compressed but retained what appeared to
be their natural shape and position. Hence to explain their appearance,
it was thought that they were water-plants, ramifying the mud in every
direction, and finally becoming overwhelmed and covered by the mud
itself. On botanical grounds, Brongniart and Lyell conjectured that they
formed the roots of other trees, and this became the more apparent as it
came to be acknowledged that the underclays were really ancient soils.
All doubt was, however, finally dispelled by the discovery by Mr Binney,
of a sigillaria and a stigmaria in actual connection with each other, in
the Lancashire coal-field.

Stigmariae have since been found in the Cape Breton coal-field, attached
to Lepidodendra, about which we have already spoken, and a similar
discovery has since been made in the British coal-fields. This,
therefore, would seem to shew the affinity of the sigillaria to the
lepidodendron, and through it to the living lycopods, or
club-mosses.

Some few species of stigmarian roots had been discovered, and various
specific names had been given to them before their actual nature was made
out. What for some time were thought to be long cylindrical leaves, have
now been found to be simply rootlets, and in specimens where these have
been removed, the surface of the stigmaria has been noticed to be covered
with large numbers of protuberant tubercles, which have formed the bases
of the rootlets. There appears to have also been some special kind of
arrangement in their growth, since, unlike the roots of most living
plants, the tubercles to which these rootlets were attached, were
arranged spirally around the main root. Each of these tubercles was
pitted in the centre, and into these the almost pointed ends of the
rootlets fitted, as by a ball and socket joint.

[Illustration: FIG. 17--_Section of stigmaria_.]

"A single trunk of _sigillaria_ in an erect forest presents an epitome of
a coal-seam. Its roots represent the _stigmaria_ underclay; its bark the
compact coal; its woody axis, the mineral charcoal; its fallen leaves and
fruits, with remains of herbaceous pl