They suddenly invade a part of North America
where there were conditions for preserving some traces of them,
but we have as yet no remains of their early forms or clue to
their place of development. We may conjecture that their
ancestors had been living in some elevated inland region during
the warmth of the Jurassic period.
As it is now known that many of the cycad-like Mesozoic plants
bore flowers--as the modern botanist scarcely hesitates to call
them--the gap between the Gymnosperms and Angiosperms is very
much lessened. There are, however, structural differences which
forbid us to regard any of these flowering cycads, 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.
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