s_
(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. Of willows (Salix) the
same two works enumerate _fifteen_ and _thirty-one_ species
respectively. The hawkweeds (Hieracium) are equally puzzling, for while
Mr. Bentham admits only seven British species, Professor Babington
describes no less than thirty-two, besides several named varieties.

A French botanist, Mons. A. Jordan, has collected numerous forms of a
common little plant, the spring whitlow-grass (Draba verna); he has
cultivated these for several successive years, and declares that they
preserve their peculiarities unchanged; he also says that they each come
true from seed, and thus possess all the characteristics of true
species. He has described no less than fifty-two such species or
permanent varieties, all found in the south of France; and he urges
botanists to follow his example in collecting, describing, and
cultivating all such varieties as may occur in their respective
districts. Now, as the plant is very common almost all over Europe and
ranges from North America to the Himalayas, the number of similar forms
over this wide area would probably have to be reckoned by hundreds if
not by thousands.

The class of facts now adduced must certainly be held to prove that in
many large genera and in some single species there is a very large
amount of variation, which renders it quite impossible for experts to
agree upon the limits of species. We will now adduce a few striking
cases of individual variation.

The distinguished botanist, Alp. de Candolle, made a special study of
the oaks of the whole world, and has stated some remarkable facts as to
their variability. He declares that on the same branch of oak he has
noted the following variations: (1) In the length of the petiole, as one
to three; (2) in the form of the leaf, being either elliptical or
obovoid; (3) in the margin being entire, or notched, or even pi