Of about 180,000 species of plants in nature to-day
more than 100,000 are Angiosperms; yet up to the end of the
Jurassic not a single true Angiosperm is found in the geological
record.
This is a broad manifestation of evolution, but it is not quite
an accurate statement, and its inexactness still more strongly
confirms the theory of evolution. Though the Primary Era was
predominantly the age of Cryptogams, we saw that a very large
number of seed-bearing plants, with very mixed characters,
appeared before its close. It thus prepares the way for the
cycads and conifers and ginkgoes of the Mesozoic, which we may
conceive as evolved from one or other branch of the mixed
Carboniferous vegetation. We next find that the Mesozoic is by no
means purely an age of Gymnosperms. I do not mean merely that the
Angiosperms appear in force before its close, and were probably
evolved much earlier. The fact is that the Gymnosperms of the
Mesozoic are often of a curiously mixed character, and well
illustrate the transition to the Angiosperms, though they may not
be their actual ancestors. This will be clearer if we glance in
succession at the various types of plant which adorned and
enriched the Jurassic world.
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