e stems are longitudinally
ribbed, with transverse joints at regular intervals, these joints
giving origin to a whorl or branchlets, which mayor may not give
origin to similar whorls of smaller branchlets still. The stems,
further, were hollow, with transverse partitions at the joints,
and having neither true wood nor bark, but only a thin external
fibrous shell. There can be little doubt but that the _Calamites_
are properly regarded as colossal representatives of the little
Horse-tails (_Equisetaceoe_) of the present day. They agree with
these not only in the general details of their organisation, but
also in the fact that the fruit was a species of cone, bearing
"spore-cases" under scales. According to Principal Dawson, the
_Calamites_ "grew in dense brakes on the sandy and muddy flats,
subject to inundation, or perhaps even in water; and they had
the power of budding out from the base of the stem, so as to
form clumps of plants, and also of securing their foothold by
numerous cord-like roots proceeding from various heights on the
lower part of the stem."

[Illustration: Fig. 110.--_Lepidodendron Sternbergii_, Carboniferous,
Europe. The central figure represents a portion of the trunk with
its branches, much reduced in size. The right-hand figure is
a portion of a branch with the leaves partially attached to it;
and the left-hand figure represents the end of a branch bearing
a cone of fructification.]

The _Lepidodendroids_, represented mainly by the genus
_Lepidodendron_ itself (fig. 110), were large tree-like plants,
which attain their maximum in the Carboniferous period, but which
appear to commence in the Upper Silurian, are well represented in
the Devonian, and survive in a diminished form into the Permian.
The trunks of the larger species of _Lepidodendron_ at times
reach a length of fifty feet and upwards, giving off branches in
a regular bifurcating manner. The bark is marked with numerous
rhombic or oval scars, arranged in quincunx order, and indicating
the points where the long, needle-shaped leaves were formerly
attached. The fruit consisted of cones or spikes, carried at the
ends of the branches, and consisting of a central axis surrounded
by overlapping scales, each of which supports a "spore-case"
or seed-vessel. These cones have commonly been described under
the name of _Lepidostrobi_. In the structure of the trunk there
is nothing comparable to what is found in existing trees, there
being a thick