FLORAS OF DIFFERENT COUNTRIES. *J49 



elk, for instance, livos in the Scandinavian peninsula, almost 

 ten degrees further north than in the interior of Siberia, where 

 the line of equal winter temperature is so remarkably concave. 

 Plants migrate in the germ ; and, in the case of many species, 

 the seeds are furnished with organs adapting them to be con- 

 veyed to a distance through the air. When once they have 

 taken root, they become dependent on the soil and on the 

 fetrata of air surrounding them. Animals, on the contrary, can 

 at pleasure migrate from the equator toward the poles ; and 

 this they can more especially do where the isothermal lines 

 are much inflected, and where hot summers succeed a great 

 degree of winter cold. The royal tiger, which in no respect 

 dihers from the Bengal species, penetrates every summer into 



ing maintained by a transported flora, for the transmission of which 1 

 have shown we can not account by an appeal to unquestionable geo- 

 logical events. In the case of the Alps and Carpathians, and some other 

 mountain ranges, we find the law maintained partly by a representa- 

 tive flora special in its region, i. e., by specific centers of their own, 

 aid partly by an assemblage more or less limited in the several ranges 

 of identical species, these latter in several cases so numerous that or- 

 dinary modes of transportation now in action can no more account for 

 their presence than they can for the presence of a Norwegian flora on 

 the British mountains. Now I ain prepared to maintain that the same 

 means which introduced a sub-Arctic (now mountain) flora into Britain, 

 acting at the same epoch, originated the identity, as far as it goes, of 

 the Alpine floras of Middle Europe and Central Asia ; for, now that we 

 know the vast area swept by the glacial sea, including almost the whole 

 of Central and Northern Europe, and belted by land, since greatly up- 

 lifted, which then presented to the water's edge those climatal condi- 

 tions for which a sub-Arctic flora — destined to become Alpine — was 

 epecially organized, the difliculty of deriving such a flora from its par- 

 ent north, and of diff'asing it over the snowy hills bounding this glacial 

 ocean, vanishes, and the presence of identical species at such distant 

 points remain no longer a mystery. Moreover, when we consider that 

 the greater part of the northern hemisphere was under such climatal 

 conditions during the epoch referred to, the undoubted evidences of 

 which have been made known in Europe by numerous British and 

 Continental observers, on the bounds of Asia by Sir Roderick Murchi- 

 son, in America by Mr. Lyell, Mr. Logan, Captain Bayfield, and oth- 

 ers, and that the botanical (and zoological as well) region, essentially 

 northern and Alpine, designated by Professor Schouw that 'of saxi- 

 frages and mosses,' and first 'n his classification, exists now only on 

 the flanks of the great area which suffered such conditions; and that, 

 though similar conditions reappear, the relationship of Alpine and Arctic 

 vegetation in the southern hemisphere, with that in the northern, is 

 entirely maintained by representative, and not by identical species (the 

 representative, too, being in great part generic, and not specific), the 

 general truth of my explanation of Alpine floras, including identical 

 species, becomas so strong, that the view proposed acquires fair claims 

 to be ranked as a theory, and not considered merely a convenient ox 

 bold hy[)othe.sij "] — Tr. 



