In their general appearance the _Lepidodendra_ bring to mind
the existing Araucarian Pines; but they are true "Cryptogams,"
and are to be regarded as a gigantic extinct type of the modern
Club-mosses (_Lycopodiaceoe_). They are amongst the commonest
and most characteristic of the Carboniferous plants; and the
majority of the "spore-cases" so commonly found in the coal appear
to have been derived from the cones of Lepidodendroids.
The so-called _Sigillanoids_, represented mainly by _Sigillaria_
itself (fig. 111), were no less abundant and characteristic of
the Carboniferous forests than the _Lepidodendra_. They commence
their existence, so far as known, in the Devonian period, but
they attain their maximum in the Carboniferous; and--unlike the
Lepidodendroids--they are not known to occur in the Permian period.
They are comparatively gigantic in size, often attaining a height
of from thirty to fifty feet or more; but though abundant and
well preserved, great divergence of opinion prevails as to their
true affinities. The _name_ of Sigillarioids (Lat. _sigilla_,
little seals or images) is derived from the fact that the bark
is marked with seal-like impressions or leaf-scars (fig. 111).
[Illustration: Fig. 111.--Fragment of the external surface of
_Sigillaria Groeseri_, showing the ribs and leaf-scars. The left-hand
figure represents a small portion enlarged.
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