aking, been in accordance
with the theory of evolution. Beyond this, however, the facts were very
puzzling. The highest cryptogams--ferns, lycopods, and
equisetaceae--appeared suddenly, and in immense profusion in the Coal
formation, at which period they attained a development they have never
since surpassed or even equalled; while the highest plants--the
dicotyledonous and monocotyledonous angiosperms--which now form the bulk
of the vegetation of the world, and exhibit the most wonderful
modifications of form and structure, were almost unknown till the
Tertiary period, when they suddenly appeared in full development, and,
for the most part, under the same generic forms as now exist.

During the latter half of the present century, however, great additions
have been made to our knowledge of fossil plants; and although there
are still indications of vast gaps in our knowledge, due, no doubt, to
the very exceptional conditions required for the preservation of plant
remains, we now possess evidence of a more continuous development of the
various types of vegetation. According to Mr. Lester F. Ward, between
8000 and 9000 species of fossil plants have been described or indicated;
and, owing to the careful study of the nervation of leaves, a large
number of these are referable to their proper orders or genera, and
therefore give us some notion--which, though very imperfect, is probably
accurate in its main outlines--of the progressive development of
vegetation on the earth.[191] The following is a summary of the facts as
given by Mr. Ward:--

The lowest forms of vegetable life--the cellular plants--have been found
in Lower Silurian deposits in the form of three species of marine algae;
and in the whole Silurian formation fifty species have been recognised.
We cannot for a moment suppose, however, that this indicates the first
appearance of vegetable life upon the earth, for in these same Lower
Silurian beds the more highly organised vascular cryptogams appear in
the form of rhizocarps--plants allied to Marsilea and Azolla,--and a
very little higher, ferns, lycopods, and even conifers appear. We have
indications, however, of a still more ancient vegetation, in the
carbonaceous shales and thick beds of graphite far down in the Middle
Laurentian, since there is no other known agency than the vegetable cell
by means of which carbon can be extracted from the atmosphere and fixed
in the solid state. These great beds of graphite, th