BRITISH FOREST TREES 223 



2. ALDER, COMMON OR BLACK ALDER (Betula alnus, 

 L. = ALNUS GLUTINOSA, Gaert.). 



Distribution. The alder is found in moist situations 

 throughout nearly the whole of Europe from Asia Minor and 

 the Caucasus up to the 62 of latitude on the average ; it is 

 also indigenous to Siberia, to Japan, and to Algiers. In 

 Norway it ascends to 1,080 feet above the sea-level, in the 

 Harz mountains to 2,170 feet, in the Bavarian Alps to 2,800, 

 and in the Tyrolese Alps to 4,100 feet. 1 At anything ap- 

 proaching to these limits, however, its development is not 

 normal, it being essentially a tree of the low-lying lands, 

 marshes, and riverine stretches, and of the tracts adjacent to 

 the sea-coast, especially when they are subject to freshwater 

 inundations rich in silt. On fen soil in the Baltic pro- 

 vinces of northern Germany it is often found in pure forests 

 of scores of square miles in extent, and at other times in 

 extensive mixed forests along with birch, aspen, ash, &c. 



When met with on the uplands and hilly tracts, it is nearly 

 always in low-lying wet localities, in the valleys, coombs, and 

 dingles formed by the undulations of the hill-sides, and kept 

 wet and marshy by springs, or owing to an undrained, im- 

 permeable or impervious subsoil. 



Tree-form and Root-system. When grown in close canopy, 

 and to a considerable extent even when grown in an isolated 

 position, the alder develops a straight bole, with an easily 

 traceable ascending axis. In this respect it somewhat 

 resembles the conifers, more so indeed than any other broad- 

 leaved species, but in their approach to a cylindrical form of 



1 liurckhardt, .SVic?// uiui P/lan^ai, 1880, p. 209, states, however, that 

 tliis alder is not indigenous to the Alps, " One sees here, especially in 

 the valleys, only the white alder (A. incatta, D C. ), and higher up the 

 bushy mountain alder" (A. viridis, D C.). 



