212 BRITISH FOREST TREES 



across Russia to Siberia, Blasius found that B. pubescens 

 was the variety of most frequent occurrence. Gayer again 

 states that B. verrucosa goes much further to the north and 

 east, whilst B. pubescens extends further towards south and 

 west. 



The macroscopic differences between these two varieties of B. alba 

 are : 



verrucosa. Leaves and young twigs warty ; leaves without hairs ; 

 lower portion of bole with coarse, blackish, deeply 

 fissured bark. This is the usual variety. 



pubescens. Leaves and twigs without warts ; young leaves, petioles, 

 and shoots covered with velvet-like hairs ; bark 

 remaining white and smooth at lower extremity of 

 the stem. 



On the mountains of southern Europe there is no zone 

 of birch corresponding with its extension towards the colder, 

 higher northern latitudes, but it remains rather a distinctive 

 tree of the plains and uplands. In Scandinavia, though 

 more particularly in northern Russia, it forms extensive 

 forests, and attains a high degree of development. In 

 northern Germany it often forms forests along with the 

 aspen, the alder, and the Scots pine. 



Tree-form and Root-system. In its northern home the 

 birch develops a tall, straight, fairly cylindrical stem, with 

 a well-formed, but thinly-foliaged, oval crown borne by 

 comparatively few branches, though in Scotland, and 

 throughout central Europe, its growth is usually neither 

 straight, nor approaching the cylindrical form of bole so 

 prized in timber trees. On suitable soils it has a tendency to 

 extend its crown laterally, and to assume a somewhat circular 

 to obovate outline of canopy, whilst in isolated positions 

 a lively and vigorous branch development often gives it trie 

 pendulous appearance known as a "hanging or drooping 

 birch." 



