o have existed during the
Carboniferous period is so great, that nothing more can be done
here than to notice briefly the typical and characteristic _groups_
of these--such as the Ferns, the Calamites, the Lepidodendroids,
the Sigillarioids, and the Conifers.

[Illustration: Fig. 108.--_Odontopteris Schlotheimii_. Carboniferous,
Europe and North America.]

[Illustration: Fig. 109.--_Calamites cannoeformis_. Carboniferous
Rocks, Europe and North America.]

In accordance with M. Brongniart's generalisation, that the Palaeozoic
period is, botanically speaking, the "Age of Acrogens," we find
the Carboniferous plants to be still mainly referable to the
Flowerless or "Cryptogamous" division of the vegetable kingdom.
The flowering or "Phanerogamous" plants, which form the bulk
of our existing vegetation, are hardly known, with certainty,
to have existed at all in the Carboniferous era, except as
represented by trees related to the existing Pines and Firs,
and possibly by the Cycads or "false palms."[18] Amongst the
"Cryptogams," there is no more striking or beautiful group of
Carboniferous plants than the _Ferns_. Remains of these are found
all through the Carboniferous, but in exceptional numbers in
the Coal-measures, and include both herbaceous forms like the
majority of existing species, and arborescent forms resembling
the living Tree-ferns of New Zealand. Amongst the latter, together
with some new types, are examples of the genera _Psaronius_ and
_Caulopteris_, both of which date from the Devonian. The simply
herbaceous ferns are extremely numerous, and belong to such
widely-distributed and largely-represented genera as _Neuropteris,
Odontopteris_ (fig. 108), _Alethopteris, Pecopteris, Sphenopteris,
Hymenophyllites_, &c.

[Footnote 18: Whilst the vegetation of the Coal-period was mainly
a terrestrial one, aquatic plants are not unknown. Sea-weeds
(such as the _Spirophyton cauda-Galli_) are common in some of
the marine strata; whilst coal, according to the researches of
the Abbe Castracane, is asserted commonly to contain the siliceous
envelopes of Diatoms.]

The fossils known as _Calamites_ (fig. 109) are very common in
the Carboniferous deposits, and have given occasion to an abundance
of research and speculation. They present themselves as prostrate
and flattened striated stems, or as similar uncompressed stems
growing in an erect position, and sometimes attaining a length
of twenty feet or more. Externally, th