order, those forms which varied upon the same stock, he next had to combine similarly various forms which, though not found associated upon tho samo branch, were thoroughly blended by intermediato degrees:

"The lower groups (varieties or races) being thus constituted, I have given the rank of species to the groups next abovo these, which differ in other respects, I. e., either in characters which were not found united upon certain individuals, or in those which do not show transitions from one individual to another. For the oaks of regions sufficiently known, the species thus formed rest upon satisfactory bases, of which the proof càn be furnislied. It is quito otherwise with those which aro represented in our herbaria by single or few specimens. Theso aro provisional species-species which may hereafter fall to the rank of simple varieties. I have not been inclined to prejudge such questions; indeed, in this regard, I am not disposed to follow those authors whose tendency is, as they say, to reunito species. I never reunito them without proof in each particular case; while the botanists to whom I refer do so on the ground of analogous variations or transitions occurring in the same genus or in the same family. For example resting on the fact that Quercus Iler, Q. coccifera, Q. acutifolia, etc., have the leaves sometimes entire and sometimes toothed upon the same branch, or present transitions from one tree to another, I might readily have united my Q. Tlapurakuensis to Q. Sartorii of Liebmann, since these two differ only in their entire or their toothed leaves. From the fact that the length of the peduncle varies in Q. Robur and many other oaks, I might have combined Q. Seemannii Liebm. with Q. salicifolia Néo. I have not admitted these inductions, but have demanded visible proof in each particular case. Many species are thus left as provisional; but, in proceeding thus, the progress of the science will be more regular, and the synonymy less dependent upon the caprice or the theoretical opinions of each author."

This is safe and to a certain degrco judicious, no doubt, as respects published species. Once admitted,

they may stand until they are put down by evidence, direct or circumstantial. Doubtless a species may rightfully bo condemned on good circumstantial evidence. But what courzo does Do Candollo pursuo in the case of every-day occurrenceo to most working botanists, having to elaborato collections from coun tries not so well explored as Europo-when the forms in question, or one of the two, aro as yet unnamed ? Does he introduce as a new species every form which he cannot connect by ocular proof with a near relative, from which it differs only in particulars which he sees are inconstant in better known species of the same group? We suppose not. But, if he does, little improvement for the future upon the state of things revealed in the following quotation can be expected:

"In the actual state of our knowledge, after having seen. nearly all the original specimens, and in some species as many us two hundred representatives from different localities, I estimato that, out of the three hundred species of Cupulifera which will be enumerated in the Prodromus, two-thirds at least are provisional species. In general, when we consider what a multitude of species were described from a single specimen, or from the forms of a single locality, of a single country, or are badly described, it is difficult to believe that above one-third of the actual species in botanical works will remain unchanged."

Such being the results of the want of adequate knowledge, how is it likely to be when our knowledge is largely increased? The judgment of so practised a botanist as De Candolle is important in this regard, and it accords with that of other botanists of equal experience.

"They are mistaken," he pointedly asserts, "who repeat that the greater part of our species are clearly

limited, and that the doubtful species aro in a feeblo minority. This seemed to bo true, so long as a genus was imperfectly known, and its species were founded upon few specimens, that is to say, were provisional, Just as we come to know them better, intermediato 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 definito their limitation, or, in other terms, the fewer the ambiguous or doubtful forms; that genera aro moro 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 brought intermediate forms to light, perplexing to the systematist. "They are mistaken," we think moro than one systematic botanist will say," who repeat that the greater part of our natural orders and tribes aro absolutely limited," however we may agree that wo will limit them. Provisional genera we suppose are proportionally hardly less common than provisional species; and hundreds of genera are 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 specios aro just those which present the greatest number of spontaneous varieties and sub-varioties. Tho maximum is found in Q. Robur, with twenty-eight varieties, all spontaneous. Of Q. Lusi tanica eleven varieties are enumerated, of Q. Calliprinos ten, of Q. coccifera cight, etc. And he sig nificantly 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 Cupuliferæ, 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 limita tion, 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 ho 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 indicato 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 the most accordant with the known facts in paleontology, geographical botany and zoology, of anatomical structure and classification: but direct proof of it is wanting, and moreover, it true, it must have taken place very slowly; so slowly, indeed, that its effects are discernible only after a lapro of time far longer than our historic epoch."

In contemplating the present state of the species of Cupulifera in Europe, De Candolle comes to the conclusion that, while the beech is increasing, and extending its limits southward and westward (at the expense of Conifere and birches), the common oak, to some extent, and the Turkey oak decidedly, are diminishing and retreating, and this wholly irrespectivo of man's agency. This is inferred of the Turkey oak from the great gaps found in its present geographical arca, which are otherwise inexplicable, and which ho regards as plain indications of a partial extinction.