Dense thickets, like cane or bamboo brakes, were composed of thick
clumps of CALAMITES, whose slender, jointed stems shot up to a
height of forty feet, and at the joints bore slender branches set
with whorls of leaves. These were close allies of the Equiseta or
"horsetails," of the present; but they bore characteristics of
higher classes in the woody structures of their stems.

There were also vast monotonous forests, composed chiefly of trees
belonging to the lycopods, and whose nearest relatives to-day are
the little club mosses of our eastern woods. Two families of
lycopods deserve special mention,--the Lepidodendrons and the
Sigillaria.

The LEPIDODENDRON, or "scale tree," was a gigantic club moss fifty
and seventy-five feet high, spreading toward the top into stout
branches, at whose ends were borne cone-shaped spore cases. The
younger parts of the tree were clothed with stiff needle-shaped
leaves, but elsewhere the trunk and branches were marked with
scalelike scars, left by the fallen leaves, and arranged in spiral
rows.

The SIGILLARIA, or "seal tree," was similar to the Lepidodendron,
but its fluted trunk divided into even fewer branches, and was
dotted with vertical rows of leaf scars, like the impressions of a
seal.

Both Lepidodendron and Sigillaria were anchored by means of great
cablelike underground stems, which ran to long distances through
the marshy ground. The trunks of both trees had a thick woody
rind, inclosing loose cellular tissue and a pith. Their hollow