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Show 184 DARWINIAN A. limited, and "that the doubtful species are in a feeble minority. This seemed to be. true, s? long as a genus was imperfectly known, and 1ts spemcs were f?~nded upon few specimens, tl~at is to say, were. proVJ.siO~al. Just as we come to know them better, mtermed1ate forms flow in, and doubts as to specific limits aug-ment." De Candolle insists, indeed, in this connection, that the higher the rank of the groups, the more definite their limitation, or, in other terms, the fewer the ambiguous or doubtful forms ; that genera are more strictly limited than species, tribes than genera, orders than tribes etc. We are not convinced of-this. Often where it has appeared to be.so, advancing discovery has brouO'ht intermediate forms to light, perplexing to the syste~atist. "They are mistaken," we think more than one systematic botanist will say," who repeat that the greater part of our natural orders and tribes are absolutely limited," however we may agree that we will limit them. Provisional genera we suppose are proportiona11y hardly less common than provisional species; and hundreds of genera are kept up on considerations of gen.eral propriety or general convenience, although well known to shade off into.adjacent ones by complete gradations. Somewhat of th1s 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 definit~ness .. Singular as it may appear, we have heard 1t demed that spontaneous varieties occur. De Candolle makes SPECIES AS TO VARIATION, ETC. 185 the important announcement that, in the oak genus, the best known species are just those which present the greatest number of spontaneous varieties ang 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 Candone'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 Cupuliferm, 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 Ter-. tiary epoch, since which time they have been subject |
