c;i:OGKAPIlY OF PLANTS. ^67 



thougli, as \vu have said, these are rather faniiUcs, as Pahiia-, 

 Scitamincae, Muscat, Myrtea?, Saphidea^, and Aiionca'; or 

 genera, as Epidcndrum, Santalum^ Olax^ Cymhidiuvi, and 

 so forth : yet there are particular species, which grow in all 

 parts of the world only between the tropics, as, for instance, 

 Heliotrop'mm Indlcum, Ageratum coni/zokles, Pist'ia stra- 

 tiotcs, Scoparia dulcis, Guilandina Bo?iduc^ Splicnoclea zey^ 

 lanica, Ahrus precatorms, Boerhavia rtwiahiUs, and so forth. 

 But most commonly there are other species, which, under 

 the same degree of latitude, supply in the new world the 

 place of related species in the old. Dnjas octopetala, in- 

 deed, grow s equally upon the mountains of Canada, and in 

 Europe ; but Dryas tenella of Pursh, which is very like the 

 former, grows only in Greenland and Labrador. Instead 

 of th.e Platanus orientalis^ there grows in North America the 

 Platanus occidcntalis ; instead of Thiiia orlenUdls, Thuia 

 occidentalis ; instead oi Pinus Ccmbra^ in Europe and Asia, 

 there grows in North America, Pinus Strobus ; instead of 

 Prunus Laurocerasus^ in Asia Minor, there grov,s under the 

 same latitude in North America, the Prunus Caroliniana. 



394. 

 There are many exceptions to this rule, however, depending 

 on circumstances that have been already noticed. In the first 

 place, countries are wont to share their Floras with neighbour- 

 ing regions, especially islands lying under the same latitude, 

 as the Azores possess the Floras of Europe and of Nortiiern 

 Africa, rather than those of America, because they are scarce- 

 ly ten degrees of longitude from the coast of Portugal. Si- 

 cily, and still more Malta, possesses a Flora made up of those 

 of the south of Europe and the north of Africa. The Aleu- 

 tian Islands share their Flora with the north-west c(Kist ot' 

 America and the north-east of Asia. But the most distant 

 countries, lying under the same latitude, may have the 

 same, or a similar vegetation, while countries, or islands 

 which lie between them, have not the least share in this ])arti- 

 cular Flora. The island of St Helena, which is scarcely 

 eighteen degrees of longitude from tlu> wcsi coast of Alrica, 



