Upwards of three hundred species of plants have been ascertained to
exist in the coal formation; but it is not necessary to suppose that
the whole contained in that system are now, or ever will be
distinguished. Experiments shew that some great classes of plants
become decomposed in water in a much less space of time than others,
and it is remarkable that those which decompose soonest, are of the
classes found most rare, or not at all, in the coal strata. It is
consequently to be inferred that there may have been grasses and
mosses at this era, and many species of trees, the remains of which
had lost all trace of organic form before their substance sunk into
the mass of which coal was formed. In speaking, therefore, of the
vegetation of this period, we must bear in mind that it may have
comprehended forms of which we have no memorial.

Supposing, nevertheless, that, in the main, the ascertained
vegetation of the coal system is that which grew at the time of its
formation, it is interesting to find that the terrestrial botany of
our globe begins with classes of comparatively simple forms and
structure. In the ranks of the vegetable kingdom, the lowest place
is taken by plants of cellular tissue, and which have no flowers,
(cryptogamia,) as lichens, mosses, fungi, ferns, sea-weeds. Above
these stand plants of vascular tissue, and bearing flowers, in which
again there are two great subdivisions; first, plants having one
seed-lobe, (monocotyledons,) and in which the new matter is added
within, (endogenous,) of which the cane and palm are examples;
second, plants having two seed-lobes, (dicotyledons,) and in which
the new matter is added on the outside under the bark, (exogenous,)
of which the pine, elm, oak, and most of the British forest-trees are
examples; these subdivisions also ranking in the order in which they