6 Origin of the British Flora. 
dispersal of the various species which constitute our flora, 
with special reference to the present and past distribution 
of the plants. Finally, I propose to give an historical 
account of each species as far back as geological evidence 
will yet allow it to be traced. 
It may be considered presumptuous to attempt such a 
task ; but, though the following Chapters are most imper- 
fect, yet they may do good by directing attention to lines 
and methods of research which are as yet little appreciated. 
The section on the geological history of our flora, being a 
record of the actual distribution in space and time of our 
plants from direct observation, will perhaps be the one to 
which botanists will most readily turn. It may be sug- 
gested, however, that the section on means of dispersal is 
equally important, and that the connexion between the 
different Chapters is so close that it is impossible properly 
to appreciate the relationship of the living plants to their 
fossil representatives without a study of the subject from 
various points. 
Though the present volume is professedly occupied with 
a discussion of the origin of the British flora, it should not 
be forgotten that in questions of geographical distribution 
it is impossible to separate animals from plants, for many 
plants are directly dependent on certain animals for means 
of dispersal. Moreover, certain animals are dispersed by 
the same means as flowering plants, have the same difficul- 
ties to contend with, are no less dependent on climatic 
conditions, and are almost equally tied to a single spot 
during the lifetime of the individual. The land mollusca 
in particular are in these respects so like the more sedentary 
species of flowering plants that I have not hesitated to 
speak of them where they help to illustrate the subject 
under consideration. Beetles, I believe, would also be of 
use ; but of this order I have unfortunately no knowledge, 
