If I get a little time I will look up the facts: though, as Dr.Hooker rightly tells me, I have no business to be running after side game of any sort, while there is so much I have to do--much more than I shall ever do probably--to finish undertakings I have long ago begun.
...As to your P.S.If you have time to send me a longer list of your protean genera, I will say if they seem to be protean here.

Of those you mention:-- Salix, I really know nothing about.
Rubus, the N.American species, with one exception, are very clearly marked indeed.
Mentha, we have only one wild species; that has two pretty well-marked forms, which have been taken for species; one smooth, the other hairy.
Saxifraga, gives no trouble here.
Myosotis, only one or two species here, and those very well marked.
Hieracium, few species, but pretty well marked.
Rosa, putting down a set of nominal species, leaves us four; two of them polymorphous, but easy to distinguish...
LETTER 339.

TO J.D.HOOKER.

Down, [1857 ?] One must judge by one's own light, however imperfect, and as I have found no other book (339/1.

A.De Candolle's "Geographie Botanique," 1855.) so useful to me, I am bound to feel grateful: no doubt it is in main part owing to the concentrated light of the noble art of compilation.