BIO-GEOLOGY. 55 
let me give you a few hare on this matter. You must 
duy the plants of enn species by species. Take Watsou's * Cybele 
Britannica’ and Moore's * Cybele Hibemnica, and let (as Mr. Matthew 
Arnold would say) joie Aistit play freely about them. Look carefully, 
too, in the case of each species, at the note on its Secale which you 
will find appended in Bentham's ‘ Handbook’ and in Hooker's * Student's 
Flora) Get all the help you can, if you ish to work the dito out, 
from foreign botanists, both European and American; and I think that, 
on the whole, you will come to some such theory as this fora general 
a platform namely, that we do not owe our flora (Beust keep to 
the flora just now) to so many different regions— or types, as Mr. Watson 
calls ER Mr. Watson makes ; ut to three, namely, a European or 
Germanie flora, from the S.E.; an Aee flora, from the S.W. ; 
Northern flora, from the N.; and that these three invaded us after ‘he 
glacial epoch, and our general flora is their result. 
But this will cause you much trouble. Before you go a step further 
you will have to eliminate from all your calculations most of the plants | 
which Watson calls glareal, i. e. found in cultivated ground about habita- 
tions. And what their limit may be I think we never r shall know. But 
of this we may be sure, that just as invading armies always pire with 
them, in forage or otherwise, some plants from their own count ry; just 
as the Cossacks, in pibe brought more than one Russian plant through 
Germany into France; just as you will inevitably have a crop of North 
German plants upon ite battle-fields of France next summer,—so do con- 
nicis races bring new plants. The Romans, during their 300 or 400 
of oceupation sc civilization, must bite br ought more species, I 
believe, Ls is dur mention. I suspect them of having brought, not 
erely the c on hedge Elm of the South, not merely the three species 
of "Nettle, ios all our red Poppies, and a great number of the weeds which 
are common in cornfields ; and when we add to them the plants ibaa 
may have been ducit by returning crusaders and pilgrims, by mo 
from every part of Europe, by Flemings or other dealers in foreign vost 
we have to cut a huge cantle out of our iran flora ; ; only, having 
no records, we hardly know where and what to cut out, 0 
we elder ones, recommend the subject to the fioe of the vide odiis, 
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 tois one of the floras, namely, the og ie for they'proba- 
bly came from the south-east, by whatever means the 
That European flora iüivaded us, ] presume, immediately after the 
i nd 
questions of interest will arise to those who will study, not merely the in- 
vasion of that truly ache flora, but the invasion of reptiles, epis 
and birds, especially birds of passage, which must have followed it as 
as the land was sutficiently covered with vegetation to support "ife. 
ictups volumes remain to be written - this subje ect. I trust that some 
of y oo” members may live to write one of them. The way to 
ei will be, mpare the flora nd fauna of this part of it very 
carefully with non of the southern and eastern counties; and then to com- 
pare them again with the fauna and flora of France, Belgium, and 
Holland, 
