CHAPTER III 



THE NUMERICAL DISTRIBUTION OF BRITISH PLANTS : 

 TEMPERATE FLORAS COMPARED 



Proceeding from the more to the less familiar regions we 

 will begin with a few of the facts as to the flora of our own 

 country. Partly owing to its insular character, and also 

 because it has few lofty mountains or extensive forests, the 

 number of species of flowering plants is somewhat (but not 

 much) below that of most continental countries of equal area. 

 It contains about 1 800 species, as a rough mean between 

 the estimates of different botanists. 1 It may seem curious 

 that there should be any such difference of opinion, but one 

 of the facts that have always been adduced as showing that 

 species are not fixed and immutable entities is the frequent 

 occurrence of varieties, which are sometimes so peculiar and 

 so apparently constant that they are treated by some botanists 

 as distinct species, by others as sub-species, and by others 

 again as forms or varieties only. These modifications of a 

 species are usually confined to a more limited area than the 

 species itself, and are occasionally connected with each other 

 or with the parent species by intermediate forms. Again, 

 when these varieties are cultivated, and especially when a 

 large number of plants are raised from their seeds, they are 

 apt to revert partially or wholly to the parent form. Another 

 source of difference of opinion among botanists is, as to the 

 treatment of those plants, found usually near human habita- 

 tions, which are supposed to have been originally introduced, 

 either purposely or accidentally, from foreign countries. 



1 In all the tables and comparisons of " Floras" in this work, unless where 

 ferns are specially noted, flowering plants only are intended, even when the term 

 '* plants " is used. 



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