otent and inferior beyond their own
domain." (Wallace, "Island Life", pages 527, 528.)

It will be noticed that in the summary I have attempted to give of the
history of the subject, efforts have been concentrated on bringing into
relation the temperate floras of the northern and southern hemispheres,
but no account has been taken of the rich tropical vegetation which
belts the world and little to account for the original starting-point
of existing vegetation generally. It must be remembered on the one hand
that our detailed knowledge of the floras of the tropics is still very
incomplete and far inferior to that of temperate regions; on the other
hand palaeontological discoveries have put the problem in an entirely
new light. Well might Darwin, writing to Heer in 1875, say: "Many
as have been the wonderful discoveries in Geology during the last
half-century, I think none have exceeded in interest your results with
respect to the plants which formerly existed in the arctic regions."
("More Letters", II. page 240.)

As early as 1848 Debey had described from the Upper Cretaceous rocks of
Aix-la-Chapelle Flowering plants of as high a degree of development
as those now existing. The fact was commented upon by Hooker ("Introd.
Essay to the Flora of Tasmania", page xx.), but its full significance
seems to have been scarcely appreciated. For it implied not merely that
their evolution must have taken place but the foundations of existing
distribution must have been laid in a preceding age. We now know
from the discoveries of the last fifty years that the remains of the
Neocomian flora occur over an area extending through 30 deg of latitude.
The conclusion is irresistible that within this was its centre of
distribution and probably of origin.

Darwin was immensely impressed with the outburst on the world of a
fully fledged angiospermous vegetation. He warmly approved the brilliant
theory of Saporta that this happened "as soon (as) flower-frequenting
insects were developed and favoured intercrossing." ("More Letters", II.
page 21.) Writing to him in 1877 he says: "Your idea that dicotyledonous
plants were not developed in force until sucking insects had been
evolved seems to me a splendid one. I am surprised that the idea never
occurred to me, but this is always the case when one first hears a
new and simple explanation of some mysterious phenomenon." ("Life
and Letters", III. page 285. Substantially the same idea had
occurred