ranked by some authors as species. Look at the common oak, how closely it
has been studied; yet a German author makes more than a dozen species out
of forms, which are almost universally considered by other botanists to be
varieties; and in this country the highest botanical authorities and
practical men can be quoted to show that the sessile and pedunculated oaks
are either good and distinct species or mere varieties.

I may here allude to a remarkable memoir lately published by A. de
Candolle, on the oaks of the whole world. No one ever had more ample
materials for the discrimination of the species, or could have worked on
them with more zeal and sagacity. He first gives in detail all the many
points of structure which vary in the several species, and estimates
numerically the relative frequency of the variations. He specifies above a
dozen characters which may be found varying even on the same branch,
sometimes according to age or development, sometimes without any assignable
reason. Such characters are not of course of specific value, but they are,
as Asa Gray has remarked in commenting on this memoir, such as generally
enter into specific definitions. De Candolle then goes on to say that he
gives the rank of species to the forms that differ by characters never
varying on the same tree, and never found connected by intermediate states.
After this discussion, the result of so much labour, he emphatically
remarks: "They are mistaken, who repeat that the greater part of our
species are clearly limited, and that the doubtful species are in a feeble
minority. This seemed to be true, so long as a genus was imperfectly
known, and its species were founded upon a few specimens, that is to say,
were provisional. Just as we come to know them better, intermediate forms
flow in, and doubts as to specific limits augment." He also adds that it
is the best known species which present the greatest number of spontaneous
varieties and sub-varieties. Thus Quercus robur has twenty-eight
varieties, all of which, excepting six, are clustered round three sub-