Page:Encyclopædia Britannica, Ninth Edition, v. 7.djvu/307

289 VEGETABLE.] DISTRIBUTION 289 the Roman period in the Danish islands, but is now extinct ; it was succeeded by the sessile-fruited oak, to be in turn supplanted by the pedunculated form of the same tree, associated with the alder, birch, and hazel. The oak is now almost supplanted by the beech. 1 According to Areschoug, the original post-glacial flora of Scandinavia has retreated to the north, and is probably still retreating, while the flora of central and south Scandinavia consists of &quot; an eastern and north-eastern vegetation, which spread into Europe after the glacial period and before the beech tree had invaded Sweden, with the admixture of more southern species, which, with the beech, have since penetrated into Sweden through Denmark.&quot; 2 The beech and the chestnut occur in Japan, and, as far as Europe is concerned, there is good reason to regard their origin as Eastern. As already pointed out, the American element in the European flora suffered severely during the glacial period, and has never since recovered itself. Japan, however, appeared to have been a great centre of preservation, and hence the numerous points of contact which its flora presents with that of the North American continent. In the New World itself, the continuity of the pre-glacial and post-glacial temperate floras has been better preserved. The following passage from an address of Asa Gray s may be quoted as giving its history in a concise form : He &quot;considered that the present vegetation or its proximate ancestry must have occupied the arctic and sub-arctic regions in Pliocene times, and that it had been gradually pushed southward as the temperature lowered and the glaciation advanced, even be yond its present habitation ; that plants of the same stock and kindred probably ranging round the arctic zone as the present arctic species do, made their forced migration southwards upon widely different longitudes, and receded more or less as the climate grew warmer ; that the general difference of climate which marks the eastern and western sides of the continents, the one extreme, the other mean, was doubtless even then established, so that the same species and the same sorts of species would be likely to secure and retain foothold in the similar climates of Japan and the Atlantic United States, but not in intermediate regions of different distribu tion of heat and moisture; so that different species of the same genus, as in Torreya, or different genera of the same group as red wood, Taxodium and Glyptostrobus, or different associations of forest- trees, might establish themselves each in the region best suited to the particular requirements, while they would fail to do so in any other.&quot; 3 The west of Europe possesses the remains of a local and probably more ancient flora of very great interest, characterized by Gorse, and allied shrubby Legiiminosoe, fleaths, Lobelias, Sibthorpias, &c. These are closely checked in any tendency towards eastern dispersion by the severity of the winter climate away from the ameliorating influence of the sea. The probability of a southern extra- tropical connection of this peculiar element in the Nor thern flora will be adverted to hereafter. The flora of the British Isles is in many respects interesting ; it is in its main features an extension of the Germanic area of the temperate flora with the presence of the western element above alluded to distinctly marked on the south-western coasts. Eriocaulon septangulare is an anomalous constituent, being limited to Ireland and a few islets on the western side of North Britain, and being otherwise an American and not a European species. 4 Its presence can hardly ba explained except by the agency of migratory birds. 3. The Mediterraneo-C aucasian flora, like the Arctic- alpine, contrasts in the most marked way with the temperate. &quot;By far the richest and most diversified in species [it comprises six-sevenths of the European flora], it is also remarkable for the 1 Lyell, Antiquity of Man, p. 9. 2 Bentham, 1. c. p. 22. 3 Dammniana, pp. 224, 225. 4 Watson, Compendium, p. 31. great variations centering round individual types, as well as for the very restricted areas occupied by a number of the most marked species ; the limits are not to be accounted for by any physical peculiarities we are acquainted with, nor perhaps to be otherwise explained than by a supposition of very great antiquity.&quot; Eastward of the Caucasus this remarkable flora dies away, reaching its eastern limit in Scinde, and the tem perate flora of Asia is only separated from the tropical by the Himalayas. Southwards its progress is arrested by the arid zone formed by the African and Arabian deserts. 5 As in the case of the Arctic flora, traces still exist of its former southern extension under the influence of a colder terrestrial climate. Adenocarpus, a characteristic Mediter ranean genus, is represented by an identical species on Kilima Njaro, near the equator, and on the Cameroons mountains, 2000 miles distant on the opposite and western side of the African continent. 6 II, THE SOUTHERN FLOBA. The Southern flora exhibits relations much, more complex than those presented by the Northern. Instead of extending over large con tinental areas it is now dismembered into isolated groups scattered over the southern hemisphere, and in both the New and Old World sending northern extensions across the equator. Five types may be briefly described, the definition of all but the first being taken from Bentham : 7 1. The Antarctic-alpine flora is the complement of the Arctic-alpine. It consists mainly of some widely distri buted northern genera such as Carex, Poa, Ranunculus, &c., with alpine types of strictly south temperate genera char acteristic of the respective localities. Hooker describes it as possessing &quot; decided Australian representatives in Cen- trolepidece and Stylidiece, commencing in Fuegia, the Falk- lauds, and Lord Auckland s and Campbell s groups, re appearing in the Alps of New Zealand, Tasmania, and Australia, and disappearing under the equator, on the Alps of Borneo.&quot; 8 2. The Australian flora is &quot;almost endemic, showing some slight connection with the New Zealand, and a few remains of former ramifications northward to some parts of the Indian Archipelago, a very few species, perhaps of modern introduction, extending to China and Japan.&quot; Bentham 9 conclusively dismisses Unger s theory of the former extension of the Australian flora into Europe in Eocene times. 3. The Andine flora, characterized by a large number of distinct genera, Fuchsia, Gaultheria, Calceolaria, ranges more or less along the whole chain, &quot;penetrating far northwards in Western America, throwing off a few branches into Eastern Asia, and at its southern extremity crossing over to New Zealand, and in smaller numbers to Tasmania, and the mountains of Victoria.&quot; 10 4. The Mexico- Calif or nian flora is &quot; represented at great distances by closely allied species of small distinct genera in Mexico and California, in the Argentine states, and in S. Africa or Australia.&quot; 11 5. The S. African flora is &quot; perhaps the richest known in proportion to its extent, and remarkably varied within its narrow limits.&quot; Its connection with other floras is very slight. That with Australia, alluded to at the commence ment, does not extend beyond groups of the highest order (in the Proteacece not merely the species but the genera 6 Bentham, Nat. Hist. Rev., 1864, p. 373. 6 Hooker in Journ. Linn. Soc. Sot., xiv. p. 144. 7 Presidential address, 1869, pp. 24, 25. 8 Introductory Essay to the Flora of Tasmania, p. 104. 9 Presidential address, 1870, pp. 12-67. 10 On the extra-tropical southern connection between America and the Old World as illustrated by the Composite, see Bentham in Journ. Linn. Soc., xiii. p. 561. 11 See also Asa Gray, Darwiniana, pp. 218, 219. VII. - 37