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equally have to bo verified inferentially. If wo still hold to the idea of Linnavus, and of Agassiz, that existing species were created independently and essentially all at once at the beginning of the present era, we could not better the propositions of Linnaeus and of Jussieu. If, on the other hand, the time has como in which we may accept, with De Candolle, their suc cessivo origination, at the commencement of the pres ent era or before, and even by derivation from other forms, then the “ in principio” of Linneus will refer to that time, whenever it was, and his proposition bo as sound and wise as ever.

In his "Géographie Botanique" (ii., 1068-1077) Do Candolle discusses this subject at length, and in tho same interest. Remarking that of the two great facts of species, viz., likeness among the individuals, and genealogical connection, zoölogists have generally preferred the latter,' while botanists have been divided in opinion, he pronounces for the former as the essential thing, in the following argumentative statement :

"Quant à moi, j'ai été conduit, dans ma definition de l'espèce, à mettro décidément la ressemblanco au-dessus de caractères do succession. Co n'est pas seulement à causo des circonstances propres au règno végétal, dont jo m'occupo exclusivement; co n'est pas non plus afin do sortir ma définition des théories et do la rendro lo plus possiblo utilo aux naturalistes descripteurs et nomenclateurs, c'est aussi par un motif philosophique. En tonto choso il faut aller au fond des questions, quand on lo peut. Or, pourquoi la reproduction est-ello possible, habituelle, fécondo indefiniment, entro des êtres organisés que nous dirons do la

1 Particularly citing Flourens: “La ressemblance n'est qu'une con. dition secondaire; la condition essentielle est In descendance; ce n'ent pas la ressemblance, c'est la succession des individus, qui falt l'espdeo,"

mbino ospêcot Parce qu'ils so rossomblont et uniquement à causo do colą. Lorsquo doux ospòcos no pouvont, ou, s'il s'agit d'animaux supérieurs, no pouvent et no veulent so croisor, c'est qu'elles sont très differentes. Si l'on obtient des croisements, c'est que les individus sont analogues; si ces croisements donment des produits féconds, c'est que les individus étaient plus analogues; al ces produits eux-mêmes sont feconds, c'est que la rossemblanco était plus grande; s'ils sont fécond habituellement et indéfluiment, c'est que la ressemblance intériouro et extérieuro était très grando. Ainsi lo degré do ressemblanco est lo fond; In reproduction on est seulement la manifestation et la mosuro, ut il est logique du placer la causo au-dessus de l'effet."

We are not yet convinced. We still hold that genealogical connection, rather than mutual resemblance, is the fundamental thing-first on the ground of fact, and then from the philosophy of the case. Practically, no botanist can say what amount of dissimilarity is compatible with unity of species; in wild plants it is sometimes very great, in cultivated races often enormous. De Candolle himself informs us that the different variations which the same oak-tree exhibits are significant indications of a disposition to set up separate varieties, which becoming hereditary may constitute a race; he evidently looks upon the extremo forms, say of Quercus Robur, as having thus originated; and on this ground, inferred from transitional forms, and not from their mutual resemblance, ho includes them in that species. This will be more apparent should the discovery of transitions, which he leads us to expect, hereafter cause the four provisional species which attend Q. Robur to be merged in that species. It may rightly be replied that this conclusion would be arrived at from the likeness step

by step in the series of forms; but the cause of the likeness hero is obvious.

"motif philosophique."

And this brings in our

Not to insist that the likeness is aftor all tho variable, not the constant, element-to learn which is tho essential thing, resemblance among individuals or their genetic connection-we have only to ask which can bo the cause of the other.

In hermaphrodite plants (the normal case), and even as the question is ingeniously put by Do Candolle in the above extract, the former surely cannot be the cause of the latter, though it may, in case of crossing, offer occasion. But, on the ground of the most fundamental of all things in the constitution of plants and animals-the fact incapable of further analysis, that individuals reproduce their like, that characteristics are inheritable-the likeness is a direct natural consequence of the genetic succession; "and it is logical to place the cause above the effect."

We are equally disposed to combat a proposition of De Candolle's about genera, elaborately argued in the "Géographie Botanique," and incidentally reaf firmed in his present article, viz., that genera are moro natural than species, and more correctly distinguished by people in general, as is shown by vernacular names. But we have no spaco left in which to present somo evidence to the contrary.

V.

SEQUOIA AND ITS HISTORY; THE RELATIONS OF NORTH AMERICAN TO NORTHEAST ASIAN AND TO TERTIARY VEGETATION.

(A PRESIDENTIal. Address to tur American Association FOR THE ADVANCEMENT OF SCIENCr, at Dunuque, August, 1872.)

THE session being now happily inaugurated, your presiding officer of the last year has only one duty to perform before he surrenders the chair to his successor. If allowed to borrow a simile from the language of my own profession, I might liken the President of this Association to a biennial plant. IIe flourishes for the year in which he comes into existence, and performs his appropriate functions as presiding officer. When the second year comes round, he is expected to blossom out in an address and disappear. Each president, as he retires, is naturally expected to contribute something from his own investigations or his own line of study, usually to discuss some particular scientifle topic.

Now, although I have cultivated the field of North American botany, with some assiduity, for more than forty years, have reviewed our vegetable hosts, and assigned to no small number of them their names and their place in the ranks, yet, so far as our own wide country is concerned, I have been to a great extent a

closet botanist. Until this summer I had not soon the Mississippi, nor set foot upon a prairic.

To gratify a natural interest, and to gain some title for addressing a body of practical naturalists and explorers, I have made a pilgrimage across the continent. I have sought and viewed in their nativo haunts many a plant and flower which for mo had long bloomed unseen, or only in the hortus siccus. I have been able to see for myself what species and what forms constitute the main features of the vegotation of each successive region, and record—as tho vegetation unerringly does-the permanent character istics of its climate.

Passing on from the eastern district, marked by its equably distributed rainfall, and therefore naturally forest-clad, I have seen the trees diminish in number, give place to wide prairies, restrict their growth to the borders of streams, and then disappear from the boundless drier plains; have seen grassy plains clango into a brown and sero desert-desert in the common sense, but hardly anywhere botanically so-havo seen a fair growth of coniferous trees adorning the moro favored slopes of a mountain-range high enough to compel summer showers; havo traversed that broad and bare elevated. region shut off on both sides by high mountains from the moisture supplied by either occan, and longitudinally intersected by sierras which seemingly remain as naked as they were born; and have reached at length the westward slopes of that high mountain-barrier which, refreshed by the Pacific, bears the noble forests of the Sierra Nevada and tho Coast Ranges, and among them trees which aro the

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