I would merely touch here upon a subject which does not belong to my own
branch of Natural History, but is of the greatest interest in botanical
research, namely, the gradation of plants in the geological ages, and
the combination of characters in some of the earlier vegetable forms,
corresponding to that already noticed in the ancient animal types. For
instance, in the Carboniferous period we have only Cryptogams, Ferns,
Lycopodiacae, and Equisetaceae. In the middle geological ages, Conifers
are introduced, the first flowering plant known on earth, but in which
the flower is very imperfect as compared with those of the higher
groups. The Coniferae were chiefly represented in the middle periods by
the Cycadae, that peculiar group of Coniferae, resembling Pines in their
structure, but recalling the Ferns by their external appearance. The
stem is round and short, its surface being covered with scars similar to
those of the Ferns; while on the summit are ten or more leaves, fan-like
and spreading when their growth is complete, but rolled up at first,
like Fern-leaves before they expand. Their fruit resembles somewhat the
Pine-Apple.
The mode of growth of the Coniferae recalls a feature of the
Equisetaceae also, in the tufts of little leaves which appear in whorls
at regular intervals along the length of the stem in proportion as
it elongates, reminding one of the articulations on the stem of the
Equisetaceae.
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