height than any similar plant now living, sometimes being as much as
eight feet high. In the nature of their stems, too, they exhibited a more
highly organised arrangement than their living representatives, having,
according to Dr Williamson, a "fistular pith, an exogenous woody stem,
and a thick smooth bark." The bark having almost al ways disappeared has
left the fluted stem known to us as the calamite. The foliage consisted
of whorls of long narrow leaves, which differed only from the fern
_asterophyllites_ in the fact that they were single-nerved. Sir William
Dawson assigns the calamites to four sub-types: _calamite_ proper,
_calamopitus, calamodendron_, and _eucalamodendron_.

[Image: FIG. 7.--Root of _Catamites Suckowii_. Coal-shale.]

[Image: FIG 8.--_Calamocladus grandis_. Carboniferous sandstone.]

Having used the word "exogenous," it might be as well to pay a little
attention, in passing, to the nomenclature and broad classification of
the various kinds of plants. We shall then doubtless find it far easier
thoroughly to understand the position in the scale of organisation to
which the coal plants are referable.

[Illustration: FIG. 9.--_Asterophyllites foliosa_. Coal-measures.]

The plants which are lowest in organisation are known as _Cellular_. They
are almost entirely composed of numerous cells built up one above the
other, and possess none of the higher forms of tissue and organisation
which are met with elsewhere. This division includes the lichens,
sea-weeds, confervae (green aquatic scum), fungi (mushrooms, dry-rot),
&c.