from the south-east; a Northern flora, from the north. These three
invaded us after the glacial epoch; and our general flora is their
result.

But this will cause you much trouble. Before you go a step farther
you will have to eliminate from all your calculations most of the
plants which Watson calls glareal, i.e. found in cultivated ground
about habitations. And what their limit may be I think we never
shall know. But of this we may be sure; that just as invading
armies always bring with them, in forage or otherwise, some plants
from their own country--just as the Cossacks, in 1815, brought more
than one Russian plant through Germany into France--just as you have
already a crop of North German plants upon the battle-fields of
France--thus do conquering races bring new plants. The Romans,
during their 300 or 400 years of occupation and civilisation, must
have brought more species, I believe, than I dare mention. I
suspect them of having brought, not merely the common hedge elm of
the south, not merely the three species of nettle, but all our red
poppies, and a great number of the weeds which are common in our
cornfields; and when we add to them the plants which may have been
brought by returning crusaders and pilgrims; by monks from every
part of Europe, by Flemings or other dealers in foreign wool--we
have to cut a huge cantle out of our indigenous flora: only, having
no records, we hardly know where and what to cut out; and can only,
we elder ones, recommend the subject to the notice of the younger
botanists, that they may work it out after our work is done.

Of course these plants introduced by man, if they are cut out, must
be cut out of only one of the floras, namely, the European; for
they, probably, came from the south-east, by whatever means they