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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 



