304 DISTRIBUTION OF PLANTS. [SECT.XXVII. 



differ more and more even in the same parallels of latitude, 

 which shows that temperature alone is not the cause of the 

 almost complete diversity of species that everywhere prevails. 

 The Floras of China, Siberia, Tartary, of the European dis- 

 trict including Central Europe, and the coast of the Mediter- 

 ranean, and the Oriental region, comprising the countries 

 round the Black and Caspian Seas, all differ in specific cha- 

 racter. Only twenty-four species were found by MM. Bon- 

 pland and Humboldt in Equinoctial America identical with 

 those of the Old World : and Mr. Brown not only found that 

 a peculiar vegetation exists in New Holland, between the 

 33rd and 35th parallels of south latitude, but that, at the 

 eastern and western extremities of these parallels, not one 

 species is common to both, and that certain genera also are 

 almost entirely confined to these spots. The number of 

 species common to Australia and Europe are only 166 out of 

 4100, and probably some of these have been conveyed thither 

 by the colonists. This proportion exceeds what is observed 

 in Southern Africa, and, from what has been already stated, 

 the proportion of European species in Equinoctial America 

 is still less. 



Islands partake of the vegetation of the nearest continents, 

 but when very remote from land their Floras are altogether 

 peculiar. The Aleutian Islands, extending between Asia 

 and America, partake of the vegetation of the northern parts 

 of both these continents, and may have served as a channel 

 of communication. In Madeira and Teneriffe, the plants of 

 Portugal, Spain, the Azores, and of the north coast of Africa 

 are found ; and the Canaries contain a great number of plants 

 belonging to the African coast. But each of these islands 

 possesses a Flora that exists nowhere else ; and St. Helena, 

 standing alone in the midst of the Atlantic Ocean, out of 

 sixty-one indigenous species, produces only two or three 

 recognised as belonging to any other part of the world. 



It appears, from the investigations of M. de Humboldt, 

 that between the tropics the monocotyledonous plants, such 



