294 BRITISH FOREST TREES 



small angle with the stem, is moderately dense, more so on 

 favourable situations than that of the common alder ; but 

 like the latter the white alder may be classed as holding an 

 intermediate position between the light-demanding and the 

 shade-bearing species of forest trees. Its root-system is 

 superficial and far-reaching ; the side-roots are studded with 

 small clusters of rootlets, sometimes of considerable length. 

 In rate of growth, and as regards its attainable dimensions, 

 it much resembles the common alder. 



Requirements as to Soil and Situation. The white alder 

 is not a denizen of the fens and the marshy tracts like the 

 common alder ; nor does it, like the latter, form pure forests 

 over areas of any considerable extent. For moist, porous 

 soil, such as is so often to be found along the banks of 

 streams and at the foot of hill-sides, it has a decided pre- 

 ference, but the soil-moisture must be water in slow motion, 

 and not altogether of a stagnant nature. On sour marshes, 

 or water-logged bogs, its growth is backward and unsatis- 

 factory in comparison with the common alder. It thrives 

 best on a rather fresh or even moist soil, not too stiff or 

 binding, moderately deep, and not wanting in loamy con- 

 stituents. Although on the whole a moisture-loving tree, it 

 is content with a much smaller amount of soil-moisture than 

 the common aider, without, however, being capable of 

 showing vigorous and energetic growth on dry soil of any 

 description. It also differs from the other species in making 

 somewhat stronger demands on the mineral strength of the 

 soil, and especially shows a certain degree of preference for 

 soils with limy admixture. Cool localities with heavy 

 humid atmosphere, such as coombs and hollows at the 

 base of hills, are better suited for its growth than more open 

 and exposed situations. 



In Switzerland the white alder does yeoman service in 

 bringing under cultivation the stony channels of disused 



