HORIZONTAL RANGE OF VEGETATION. 575 



nomic ; and so also genera, as Viola or Ranunculus. If restricted to 

 two or more divisions, the groups are dinomic, trinomic, &c. Acer- 

 acese. found in Europe, Asia, and North America, are trinomic. 



5. PHYTO-GEOGRAPHICAL DIVISION OF THE GLOBE. 



1152. The subject will be considered hi two points of view: 1. In 

 respect to the horizontal or latitudinal range of vegetation ; and 2. 

 In respect to its vertical or altitudinal range. 



1153. Horizontal Range of Vegetation. Various attempts have been 

 made to divide the globe into zones or kingdoms, founded on the char- 

 acters impressed upon them by the nature of the vegetation. Willde- 

 now, Treviranus, De Candolle, Schouw, and Meyen, have each pro- 

 posed arrangements. Those of Schouw and Meyen chiefly deserve 

 attention. 



1154. Schouw, in his divisions, proceeds on the principle of the 

 predominance of certain characteristic forms or families of plants. His 

 system is founded on the three following requisites: 1. That at least 

 one- half of the known species of plants of that part of the earth, consti- 

 tuting a botanical region, should be peculiar to it. 2. That one-fourth 

 part of the genera of the region should be peculiar to it, or at least, should 

 have so decided a maximum as to be only represented in other regions. 

 3. That individual families should either be peculiar to the region, or 

 at least reach their maximum in it. The regions are divided into pro- 

 vinces according to minor differences in the vegetation ; one-fourth 

 of peculiar species, or some peculiar genera, being sufficient to form a 

 province. 



1155. Scftouw's Phyto-Geograpluc Regions. 



1. The Region of Saxifragacece and Musci, or the Alpine Arctic 

 Flora. This region is characterized by the abundance of Mosses and 

 Lichens, the presence of Saxifragacece, Gentianacece, Caryophyllaceoe, 

 Cyperacea, Salices ; the total absence of tropical families ; a notable 

 decrease of the forms peculiar to the temperate zone ; by forests of Fir 

 and Birch ; the small number of annual plants, and the prevalence of 

 perennial species; and finally, a greater liveliness in their simple 

 colours. In this region there is no cultivation. The region is divided into 

 two provinces: 1. The province of the Carices, or the Arctic Flora, 

 which comprehends all the countries within the polar circle, with some 

 parts of America, Europe and Asia, which are to the south of it, more 

 especially Lapland, the north of Russia, Siberia, Kamschatka, New 

 Britain, Canada, Labrador, Greenland, and the mountains of Scotland 

 and Scandinavia, mean temperature 36 to 41. 2. The province of 

 Primulacece and Phyteumce, or the Alpine Flora of the south of Europe, 

 which embraces the flora of the Pyrenees, Switzerland, the Tyrol, Sa- 

 voy, the mountains of Greece, the Appenines, and probably the moun- 

 tains of Spain. Mean temperature, 47 to 66. 



