FLORISTIC REGIONS 97 



Five-sevenths of the species of the Arctic region 

 occurring in the mountains of Scandinavia, the flora 

 has been termed "Scandinavian"; and, driven south- 

 ward by the cold of the Glacial Period, it has so far 

 invaded the mountain-heights of continental areas, even 

 crossing the Tropics, that it has been said to be repre- 

 sented in all latitudes, and is often named " Arctic- 

 alpine." Hardly any of the " alpine " plants of the 

 Tropics belong, however, to Northern species. 



NORTHERN ZONE OF COLD WINTERS. The North 

 Temperate Sub-zone, also known as the " Northern Zone 

 of Cold Winters," or region of " Summer Forest," extends 

 from the northern limit of trees to about lat. 50 N. (the 

 southern border of Siberia) in Asia, to the centre of 

 European Russia, the Eastern Carpathians, Balkans, 

 Alps, and Pyrenees in Europe, whilst in North America 

 it comprises Southern Alaska, British Columbia, most 

 of Canada, and the North-eastern, Central, and North- 

 western United States. Here, though the climate varies 

 from " insular " on the west coasts to " continental " 

 towards the east, there is no real dry season, and the 

 soil is in general permanently moist from the evenly- 

 distributed rainfall. The period of growth lasts from 

 three to seven months, with its maximum in July; the 

 summers are not so dry as to parch the vegetation, but 

 the winters are so cold as to check growth, and the 

 broad -leaved Angiospermous trees are mostly tropo- 

 philous, i.e. they shed their leaves, develop cork, and 

 diminish transpiration in that half of the year, so that 

 they form " summer green " forests. 



The sub-zone has been divided into the Europceo- 

 Siberian and North American Forest Regions, its dis- 

 tinctive feature being the vast areas originally occupied 

 by forests, either " pure " or homogeneous, or made up 

 of few species of trees. On the whole, the colder 

 northern or higher districts are occupied by Conifers, 

 especially Pinus, with evergreen xerophytic leaves and 

 little undergrowth; the milder southern or lower dis- 

 tricts by deciduous catkin-bearing Dicotyledons, such 

 as Oaks, Beeches, Chestnuts, and Maples. The most 

 northern Conifers, the Larches, are, however, deciduous ; 

 the broad-leaved Birches extend beyond the Conifers 

 both in latitude and altitude; and on sandy and peaty 

 soils Conifers are characteristic even in the south. The 



