Contributions to the theory of natural selection. A series of essays ... By Alfred Russel Wallace ...

164 THE MALAYAN PAPILIONIDTE AS
general conclusion is entirely objected to by the writer
of the article in the " Natural History Review," who,
however, does not deny its applicability to the particular order under discussion, while this very difference of opinion is another proof that difficulties in
the determination of species do not, any more than
in the higher groups, vanish with increasing materials and more accurate research~
Another striking example of the same kind is seen
in the genera Rubus and Rosa, adduced by Mr.
Darwin himself; for though the amplest materials
exist for a knowledge of these groups, and the most
careful research has been bestowed upon them, yet
the various species have not thereby been accurately
limited and defined so as to satisfy the majority of
botanists. In Mr. Baker's revision of the British
Roses, just published by the Linnmean Society, the
author includes under the single species Rosa canina,
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 Continental and British
botanists.
Dr. Hooker seems to have found the same thing
in his study of the Arctic flora. For though he has
had much of the accumulated materials of his predecessors to work upon, he continually expresses himself as unable to do more than group the numerous
and apparently fluctuating forms into more or less imperfectly defined species. In his paper on the "Dis