which have been caused by the separation of the petioles or leaf-stalks,
and this gives rise to the name which the genus bears. The scars are
arranged in a spiral manner the whole of the way up the stem, and the
stems often remain perfectly upright in the coal-mines, and reach into
the strata which have accumulated above the coal-seam.

[Illustration: FIG. 11.--Cast of _lepidodendron_ in sandstone.]

Count Sternberg remarked that we are unacquainted with any existing
species of plant, which like the _Lepidodendron_, preserves at all ages,
and throughout the whole extent of the trunk, the scars formed by the
attachment of the petioles, or leaf-stalks, or the markings of the leaves
themselves. The yucca, dracaena, and palm, entirely shed their scales
when they are dried up, and there only remain circles, or rings, arranged
round the trunk in different directions. The flabelliform palms preserve
their scales at the inferior extremity of the trunk only, but lose them
as they increase in age; and the stem is entirely bare, from the middle
to the superior extremity. In the ancient _Lepidodendron_, on the other
hand, the more ancient the scale of the leaf-stalk, the more apparent it
still remains. Portions of stems have been discovered which contain
leaf-scars far larger than those referred to above, and we deduce from
these fragments the fact that those individuals which have been found
whole, are not by any means the largest of those which went to form so
large a proportion of the ancient coal-forests. The _lepidodendra_ bore
linear one-nerved leaves, and the stems always branched dichotomously and
possessed a central pith. Specimens variously named _knorria,
lepidophloios, halonia_, and _ulodendron_ are all referable to this
family.

[Illustration: FIG. 12.--_Lepidodendron longifolium._ Coal-shale.]