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. Their appearance can
be called to mind by imagining the cylindrical fruit of the maize or
Indian corn to be reduced to some three or four inches in length. The
sporangia or cases which contained the microscopic spores or seeds were
arranged around a central axis in a somewhat similar manner to that in
which maize is found. These bodies have since been found actually
situated at the end of branches of _lepidodendron_, thus placing their
true nature beyond a doubt. The fossil seeds (spores) do not appear to
have exceeded in volume those of recent club-mosses, and this although
the actual trees themselves grew to a size very many times greater than
the living species. This minuteness of the seed-germs goes to explain the
reason why, as Sir Charles Lyell remarked, the same species of
_lepidodendra_ are so widely distributed in the coal measures of Europe
and America, their spores being capable of an easy transportation by the
wind.

[Illustration: FIG. 14.--_Lepidostrobus._ Coal-shale.]

One striking feature in connection with the fruit of the _lepidodendron_
and other ancient representatives of the club-moss tribe, is that the
bituminous coals in many, if not in most, instances, are made up almost
entirely of their spores and spore-cases. Under a microscope, a piece of
such coal is seen to be thronged with the minute rounded bodies of the
spores interlacing one another and forming almost the whole mass, whilst
larger than these, and often indeed enclosing them,