ise the presence, in
the Carboniferous flora, of plants combining the characters of Ferns and
Cycads. (See especially his "Organisation of the Fossil Plants of the
Coal-Measures", Part XIII. "Phil. Trans. Royal Soc." 1887 B. page 299.)
This conclusion was first reached in the case of the genera Heterangium
and Lyginodendron, plants, which with a wholly fern-like habit, were
found to unite an anatomical structure holding the balance between
that of Ferns and Cycads, Heterangium inclining more to the former
and Lyginodendron to the latter. Later researches placed Williamson's
original suggestion on a firmer basis, and clearly proved the
intermediate nature of these genera, and of a number of others, so far
as their vegetative organs were concerned. This stage in our knowledge
was marked by the institution of the class Cycadofilices by Potonie in
1897.

Nothing, however, was known of the organs of reproduction of the
Cycadofilices, until F.W. Oliver, in 1903, identified a fossil seed,
Lagenostoma Lomaxi, as belonging to Lyginodendron, the identification
depending, in the first instance, on the recognition of an identical
form of gland, of very characteristic structure, on the vegetative
organs of Lyginodendron and on the cupule enveloping the seed. This
evidence was supported by the discovery of a close anatomical agreement
in other respects, as well as by constant association between the seed
and the plant. (F.W. Oliver and D.H. Scott, "On the Structure of the
Palaeozoic Seed, Lagenostoma Lomaxi, etc." "Phil. Trans. Royal Soc."
Vol. 197 B. 1904.) The structure of the seed of Lyginodendron, proved to
be of the same general type as that of the Cycads, as shown especially
by the presence of a pollen-chamber or special cavity for the reception
of the pollen-grains, an organ only known in the Cycads and Ginkgo among
recent plants.

Within a few months after the discovery of the seed of Lyginodendron,
Kidston found the large, nut-like seed of a Neuropteris, another
fern-like Carboniferous plant, in actual connection with the pinnules
of the frond, and since then seeds have been observed on the frond in
species of Aneimites and Pecopteris, and a vast body of evidence, direct
or indirect, has accumulated, showing that a large proportion of the
Palaeozoic plants formerly classed as Ferns were in reality reproduced
by seeds of the same type as those of recent Cycadaceae. (A summary
of the evidence will be found in the writer's ar