IO 
CHAPTER II. 
The Present Flora of Britain. 
WHEN the British Flora is carefully studied, it is found 
to be composed of numerous elements, and can be divided 
into several well-marked groups. The grouping of the 
species, however, varies according to the point from which 
they are viewed. Disregarding purely botanical affinities, 
which are not under consideration in this volume, the 
assemblages necessarily differ according as the flora is 
looked at from the standpoint of relationship of the plants 
to climatic conditions; or from the standpoint of habitat, 
including variations in soil, and shelter; or again, from 
that of local distribution. No one of these methods will 
enable the plants to be grouped into ‘provinces’ satisfactory 
for all purposes. Each set of conditions overlies and 
modifies the distribution which either of the others alone 
would tend to bring about. 
If we begin with the broadest classification, that based 
on climatic conditions, we find at once that this is not 
merely a question of average, or of extreme temperature. 
It is temperature plus amount of moisture, modified in 
various ways by the season at which the rain falls, the 
amount of sunshine, and the season at which the sun is 
felt. A flowering plant has varying needs at different 
seasons; and the satisfying of these is so essential to the 
existence of the species—not necessarily, I would remark, 
the same thing as essential to the existence of the in- 
dividual—that, if the conditions are unfavourable for any 
