[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.  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.]