occasionally naturalized in a foreign soil. 
PREFACE. 
And closely analogous to this doctrine of the | 
conformity of plants of the same natural genus to 
" each other, in this great age of improvement in 
every way, is the science which displays the actual 
geographical stations of the genera; or in other 
words, as we should rather say, the primaval di- 
spersion of the vegetable kingdom over the face of 
the earth. And this is both a novel and important 
study.. For the primitive distributions have been 
by no means vague or indeterminate; but almost 
always geographically regular ; although various 
natural and even artificial operations have, at va- 
rious epochs, very far disturbed those pristine re- 
gulations. | Such more especially, as rivers, seas, 
and floods, (and hence the wide spread of aquatic 
plants), and the dreadful concussions of geological 
catastrophes : as well as the various and extensive 
emigrations of the human race—of qu rupeds 
and birds: each more or less frequently operating 
in the wide spread of vegetable seeds: which 
thereby, wherever the climate is congenial, become 
Hence 
can the geographic botanist frequently trace the 
sites of ancient and otherwise obliterated towns 
and cottages, by the extraneous or exotic weeds 
which remain there very long after the desolation 
of the ruius they inhabit, And through such 
means, the. time perhaps may arrive, when even 
some of the most, hidden and early migrations of 
the human race, and the consequent formation of 
nations, may be faintly found. (through the vege- 
