Page:Popular Science Monthly Volume 1.djvu/749

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733
ON THE DERIVATION OF AMERICAN PLANTS.

their nearest or their only living representatives in the Atlantic States, and, when elsewhere, mainly in Eastern Asia. Several of them, or of species like them, have been detected in our Tertiary deposits west of the Mississippi by Newberry and Lesquereux. Herbaceous plants, as it happens, are rarely preserved in a fossil state, else they would probably supply additional testimony to the antiquity of our existing vegetation, its wide diffusion over the northern and more frigid zone, and its enforced migrations under changes of climate. Supposing, then, that our existing vegetation, as a whole, is a continuation of that of the Tertiary period, may we conclude that it absolutely originated then? Evidently not. The preceding Cretaceous period has furnished to Caruthers in Europe a fossil print like that of the Sequoia gigantea of the famous groves, associated with pines of the same character as those that accompany the present tree; has furnished to Heer, from Greenland, two more Sequoias, one of them identical with a Tertiary species, and one nearly allied to Sequoia languidrupii, which in turn is a probable ancestor of the Californian redwood; has furnished to Lesquereux, in North America, the remains of another ancient Sequoia, a glyptotrobus; a liquidamber, which well represents our sweet-gum-tree; oaks, analogous to living ones, leaves of a plane-tree, which are also in the Tertiary, and are scarcely distinguishable from our own Platanus Occidentalis; of a magnolia and tulip-tree; and "of a sassafras undistinguishable from our living species."

I need not continue the enumeration. The facts will justify the conclusion which Lesquereux—a very scrupulous investigator—has already announced, that "the essential types of our actual flora are marked in the Cretaceous period, and have come to us after passing, without notable changes, through the Tertiary formations of our continent." According to these views, as regards the plants, at least, the adaptation to successive times and changed conditions has been maintained, not by absolute reversals, but by gradual modifications. I, for one, cannot doubt that the present existing species are the lineal successors of those that garnished the earth in the old time before them, and that they were as well adapted to their surroundings then as those which flourish and bloom around us are to their conditions now. Order and exquisite adaptation did not wait for man's coming, nor were they ever stereotyped. Organic Nature, by which I mean the system and vitality of living things, their adaptation to each other and to the world, with all its apparent and indeed real stability, should be likened, not to the ocean, which varies only by tidal oscillations from a fixed level to which it is always returning, but rather to a river so vast that we can neither discern its shores nor reach its sources, whose onward flow is no less actual because too slow to be observed by the ephemera which hover near its surface or are borne upon its bosom. Such ideas as these, though still repugnant to some, and not long since to many, have so possessed the minds of the naturalists of