rn allies,--that it seems at least as nearly related
to the Coniferae as to its lowlier representatives, the Marsileaceae. And
it is this union of traits, pertaining to what are now widely separated
orders, that imparts to not a few of the vegetables of the Coal Measures
their singularly anomalous character.

[Illustration: Fig. 21.

EAST INDIA TREE-FERN.[7]

(_Asophila perrotetiana._)]

[Illustration: Fig. 22.

SECTION OF STEM OF TREE-FERN.[8]

(_Cyathea._)]

[Illustration: Fig. 23.]

[Illustration: Fig. 24.]

[Illustration: Fig. 25.]

[Illustration: LEPIDODENDRON STERNBERGII.[9]]

[Illustration: Fig. 26.

CALAMITES MOUGEOTII.]

[Illustration: Fig. 27.

SPHENOPHYLLUM DENTATUM.]

[Illustration: Fig. 28.

SIGILLARIA RENIFORMIS.]

Let me attempt introducing you more intimately to one of those plants
which present scarce any analogy with existing forms, and which must
have imparted so strange a character and appearance to the flora of the
Coal Measures. The Sigillaria formed a numerous genus of the
Carboniferous period: no fewer than twenty-two different species have
been enumerated in the British coal fields alone; and such was their
individual abundance, that there are great seams of coal which seem to
be almost entirely composed of their remains. At least the ancient soil
on which these seams rest, and on which their materials appear to have
been elaborated from the elements, is in many instances as thickly
traversed by their underground stems as the soil occupied by our densest
forests is traversed by the tangled roots of the trees by which it is
covered; and we often find associated with them in these cases the
remains of no other plant. The Sigillaria were remarkable for their
beautifully sculptured stems, various in their pattern, according to
their species. All were fluted vertically, somewhat like columns of the
Grecian Doric; and each flute or channel had its line of sculpture
running adown its centre. In one species (_S. flexuosa_) the sculpture
consists of round knobs, surrounded by single rings, like the heads of
the bolts of the ship carpenter; in another (_S. reniformis_) the knobs
are double, and of an oval form, somewhat resembling pairs of
kidneys,--a resemblance to which the species owes its name. In another
species (_S. catenulata_) what seems a minute chain of distinctly
formed elliptical links drops down the middle of each flute; in yet
another (_S. oculata_) the carvings are