Abstract
Department of Zoology and Botany Remarks on the Characteristic Features of North American Vegetation, by Prof. Asa Gray.—The first impression produced on a visitor from Europe to the Atlantic coast would be the similarity of the flora to that of England, many of the plants being almost or quite the same. The larger number of these are obviously introduced. The mullein, the toad-flax, the rib worts, the milfoil, the clovers, thrive by every roadside as in England, and perhaps with even greater luxuriance, the competition being less. This strongly suggests the idea that the distribution of plants is not always due so much to adaptation as to opportunity. As one proceeds westward and southward, the difference becomes more marked, the European type gradually disappearing. But as European settlements extend, the settlers carry their plants with them, and the plants are well up to the-time, and travel by rail. On the other hand, some plants, but a much smaller number, are carried from America to Europe, and naturalised there. Such are Impations fulva and Erigeron canadensis. Turning from similarities to differences, one of the first points that strikes a European visitor is the great wealth of trees and shrubs. This Prof. Gray illustrated by giving the number of European and North American species in the most important arborescent orders. The reason of this is probably to be found in the different conditions of the two continents during the period of glaciation. The flora of Europe is exceptionally poor in trees, and, on the return of a warmer climate, the return northwards of those that survived in the south was barred by the Mediterranean. The fossil remains of trees belonging to many tropical orders are found in our-Miocene and Pliocene strata. In America, on the contrary, there was nothing to prevent their gradual return from the south, and accordingly we find solitary examples, or in some cases a larger number of representatives, of many tropical orders among the trees of the Northern States. Such are Menispermum (Menispermaceæ), Liriodendron (Magnoliaceæ), Diospyros (Ebenaceæ), Tecoma (Bignoniaceæ), and many others. This difference is also promoted by the greater heat of the American summer as compared with that of Europe. On the high lands of North America are also many Arctic plants, which remained after the Glacial period had passed away; but this flora is insignificant compared with that of Europe. A few species are found on the cool shores of Lake Superior, the shores of Labrador, and certain summits of the Appalachian Mountains. One of the most interesting features of North American botany is an outlying region of a true tropical flora which extends northwards up the Atlantic coast as far as the “pine-barrens” of New Jersey. Proceeding westwards, whether in the States or in Canada, a gradual striking change is observed: not only do the European importations disappear, but European genera give place to those specially characteristic of the western con tinent. Here above all is to be observed the extraordinary wealth of Composite, which make up about one-eighth of the total phanerogamous flora of North America; great numbers of species of Aster, Solidago, Eupatormm, Silphium, and other genera. Between the wooded region of the Atlantic and the wooded region of the Pacific coast, there is an immense tract of woodless prairie land, the home of the “buffalo” and of many grasses; and in the spring the number of bright coloured herbaceous plants is also very large. These plains are destitute of water, and probably never grew trees, and are capable of growing nothing but herbaceous plants, which completely dis appear in the hot dry summer. Then comes the great chain of the Rocky Mountains, which are well wooded on their sides, and have on their summits a flora of about 200 Arctic species. When the traveller reaches the Sierra Nevada, he enters perhaps the noblest coniferous forest in the world. But while the Pacific coast is extraordinarily rich in Coniferæ, it has a smaller number of trees belonging to other orders than the Atlantic coast; the entire absence of oaks, ashes, and maples, is especially remarkable.
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The British Association: Section D—Biology. Nature 30, 573–577 (1884). https://doi.org/10.1038/030573a0
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DOI: https://doi.org/10.1038/030573a0