kept up on considerations of general propriety or general convenience, although well known to shade off into adjacent ones by complete gradations.  Somewhat of this greater fixity of higher groups, therefore, is rather apparent than real.  On the other hand, that varieties should be less definite than species, follows from the very terms employed.  They are ranked as varieties, rather than species, just because of their less definiteness.

Singular as it may appear, we have heard it denied that spontaneous varieties occur.  De Candolle makes the important announcement that, in the oak genus, the best known species are just those which present the greatest number of spontaneous varieties and sub-varieties.  The maximum is found in Q. Robur, with twenty-eight varieties, all spontaneous.  Of Q. Lusitanica eleven varieties are enumerated, of Q. Calliprinos ten, of Q. coccifera eight, * etc.  And he significantly adds that “these very species which offer such numerous modifications are themselves ordinarily surrounded by other forms, provisionally called species, because of the absence of known transitions or variations, but to which some of these will probably have to be joined hereafter.”  The inference is natural, if not inevitable, that the difference between such species and such varieties is only one of degree, either as to amount of divergence, or of hereditary fixity, or as to the frequency or rarity at the present time of intermediate forms.

This brings us to the second section of De Candolle’s article, in which he passes on, from the observation of the present forms and affinities of cupuliferous plants, to the consideration of their probable history and origin.  Suffice it to say, that he frankly accepts the inferences derived from the whole course of observation, and contemplates a probable historical connection between congeneric species.  He accepts and, by various considerations drawn from the geographical distribution of European Cupuliferae, fortifies the conclusion—­long ago arrived at by Edward Forbes—­that the present species, and even some of their varieties, date back to about the close of the Tertiary epoch, since which time they have been subject to frequent and great changes of habitation or limitation, but without appreciable change of specific form or character; that is, without profounder changes than those within which a species at the present time is known to vary.  Moreover, he is careful to state that he is far from concluding that the time of the appearance of a species in Europe at all indicates the time of its origin.  Looking back still further into the Tertiary epoch, of which the vegetable remains indicate many analogous, but few, if any, identical forms, he concludes, with Heer and others, that specific changes of form, as well as changes of station, are to be presumed; and, finally, that “the theory of a succession of forms through the deviation of anterior forms is the most natural hypothesis, and