From the above considerations as to the characters and
distribution of living Ferns, M. Ad. Brongniart has applied
himself with much ingenuity, to illustrate the varying condition
and climate of our Globe, during the successive periods
of geological formations. Finding that the fossil remains of
Ferns decrease continually in number, as we ascend from
the most ancient to the most recent strata, he founds upon
this fact an important conjecture, with respect to the successive
diminutions of temperature, and changes of climate,
which the earth has undergone. Thus, in the great Coal
formation there are about 120 known species of Ferns, forming
almost one half of the entire known Flora of this formation;
these species represent but a small number of the forms
which occur among living Ferns, and nearly all belong to
the Tribe of Polypodiaceæ, in which Tribe we find the
greater number of existing arborescent species.[1] Fragments
of the stems of arborescent Ferns occur occasionally
in the same formation. M. Brongniart considers these circumstances
as indicating a vegetation, analogous to that of
the Islands in the equinoctial regions of the present Earth;
and infers that the same conditions of Heat and Humidity
which favour the existing vegetation of these islands, prevailed
in still greater degree during the formation of the
Carboniferous strata of the Transition Series.
hemisphere, and one species is found in New Zealand as far south as lat. 46°. See Brown in Appendix to Flinders's Voyage.
- ↑ In Plate 1, figs. 7, and 37, represent two of the graceful forms of arborescent Ferns which adorn our modern tropics, where they attain the height of forty and fifty feet.
An arborescent Fern forty-five feet high (Asophila brunonianan) from Silhet in Bengal, may be seen in the staircase of the British Museum. The stems of these Ferns are distinguished from those of all arborescent Monocotyledonous plants, by the peculiar form and disposition of the scars, from which the Petioles or leaf stalks have fallen off. In Palms and other arborescent Monocotyledons, the leaves, or Petioles, embrace the stem and leave broad transverse scars, or rings, whose longer diameter is horizontal. In the case of Ferns alone, with the single exception
