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_The Variability of Plants._
The variability of plants is notorious, being proved not only by the
endless variations which occur whenever a species is largely grown by
horticulturists, but also by the great difficulty that is felt by
botanists in determining the limits of species in many large genera. As
examples we may take the roses, the brambles, and the willows as well
illustrating this fact. In Mr. Baker's _Revision of the British Roses_
(published by the Linnean Society in 1863), he includes under the single
species, Rosa canina--the common dog-rose--no less than twenty-eight
named _varieties_ distinguished by more or less constant characters and
often confined to special localities, and to these are referred about
seventy of the _species_ of British and continental botanists. Of the
genus Rubus or bramble, _five_ British species are given in Bentham's
_Handbook of the British Flora_, while in the fifth edition of
Babington's _Manual of British Botany_, published about the same time,
no less than _forty-five_ species are described.


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