The Story of a Piece of Coal | Page 6

| |
| Monocotyledons |Palms, lilies,
|Endogens |
| | grasses
| |
| Dicotyledons |Most European
|Exogens |
| | trees and shrubs
| |

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Adolphe Brongniart termed the coal era the "Age of Acrogens,"
because, as we shall see, of the great predominance in those times of
vascular cryptogamic plants, known in Dr Lindley's nomenclature as
"Acrogens."
[Illustration: FIG. 10.--_Spenophyllum cuneifolium._ Coal-shale.]
Two of these families have already been dealt with, viz., the ferns
(_felices_), and the equisetums, (calamites and _equisetites_), and we
now have to pass on to another family. This is that which includes the
fossil representatives of the Lycopodiums, or Club-mosses, and which
goes to make up in some coals as much as two-thirds of the whole mass.
Everyone is more or less familiar with some of the living Lycopodiums,
those delicate little fern-like mosses which are to be found in many a
home. They are but lowly members of our British flora, and it may
seem somewhat astounding at first sight that their remote ancestors
occupied so important a position in the forests of the ancient period of
which we are speaking. Some two hundred living species are known,
most of them being confined to tropical climates. They are as a rule,
low creeping plants, although some few stand erect. There is room for
astonishment when we consider the fact that the fossil representatives
of the family, known as _Lepidodendra_, attained a height of no less
than fifty feet, and, there is good ground for believing, in many cases, a

far greater magnitude. They consist of long straight stems, or trunks
which branch considerably near the top. These stems are covered with
scars or scales, 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.]
[Illustration: FIG. 13.--Lepidodendron aculeatum in sandstone.]
In some strata, as for instance that of the Shropshire coalfield,
quantities of elongated cylindrical bodies known as lepidostrobi have

been found, which, it was early conjectured, were the fruit of the giant
club-mosses about which we have just been speaking.