s, which we have yet found, as the ancestors of the
Angiosperms. The most reasonable view seems to be that a small and local
branch of these primitive flowering plants was evolved, like the rest,
in the stress of the Permian-Triassic cold; that, instead of descending
to the warm moist levels with the rest at the end of the Triassic, and
developing the definite characters of the cycad, it remained on the
higher and cooler land; and that the rise of land at the end of the
Jurassic period stimulated the development of its Angiosperm features,
enlarged the area in which it was especially fitted to thrive, and so
permitted it to spread and suddenly break into the geological record as
a fully developed Angiosperm.

As the cycads shrank in the Cretaceous period, the Angiosperms deployed
with great rapidity, and, spreading at various levels and in different
kinds of soils and climates, branched into hundreds of different types.
We saw that the oak, beech, elm, maple, palm, grass, etc., were well
developed before the end of the Cretaceous period. The botanist divides
the Angiosperms into two leading groups, the Monocotyledons (palms,
grasses, lilies, orchises, irises, etc.) and Dicotyledons (the vast
majority), and it is now generally believed that the former were
developed from an early and primitive branch of the latter. But it is
impossible to retrace the lines of development of the innumerable types
of Angiosperms. The geologist has mainly to rely on a few stray leaves
that were swept into the lakes and preserved in the mud, and the
evidence they afford is far too slender for the construction of
genealogical trees. The student of living plants can go a little
further in discovering relationships, and, when we find him tracing such
apparently remote plants as the apple and the strawberry to a common
ancestor with the rose, we foresee interesting possibilities on the
botanical side. But the evolution of the Angiosperms is a recent and
immature study, and we will be content with a few reflections on the
struggle of the various types of trees in the changing conditions of
the Tertiary, the development of the grasses, and the evolution of
the flower. In other words, we will be content to ask how the modern
landscape obtained its general vegetal features.

Broadly speaking, the vegetation of the first part of the Tertiary Era
was a mixture of sub-tropical and temperate forms, a confused mass of
Ferns, Conifers, Ginkgoales, Monoco