224 BRITISH FOREST TREES 



the stem it falls far behind. Its branch development is slight, 

 whilst the foliage forms a somewhat light crown confined 

 to the uppermost portion of the stem, and bluntly conical in 

 general outline. On the cessation of activity of growth in 

 height, the upper portion of the stem tends more towards 

 branch formation and ramification, whilst the crown in 

 extending assumes a somewhat blunted and flatter form. 



In root-system it differs from other trees by having no 

 proper tap-root, but in sending out instead a number of 

 comparatively weak strands from the short main root : these 

 work their way down to the subsoil, and there ramify into 

 long stringy rootlets, which determine its claim to rank as an 

 essentially deep-rooting species. 



Requirements as to Soil and Situation. The demands 

 made by the alder as to atmospheric warmth are by no means 

 so great as those made in regard to atmospheric moisture. It 

 attains normal development both in warm and in cold 

 climates, but it cannot thrive in dry localities, and attains 

 its best growth in a damp insular climate, and in situations 

 which, from local causes, have great relative humidity. For 

 the proper normal and unhindered development of its 

 peculiar root-system, depth of soil is essentially necessary ; 

 swampy tracts with shallow soil and impermeable subsoil of 

 moorpan, tenacious clay, or undecomposed, unfissured rocks, 

 are not the situations suitable to it. At the same time it 

 demands a greater degree of soil moisture than can be borne 

 by the majority of other timber trees, and thrives best when 

 both soil and subsoil are moist. When the amount of 

 moisture is so great as to render the soil wet during the dry 

 period of the year, it can no longer be expected that the 

 alder will attain its normal development. This is more 

 especially the case if the water be stagnant, for when the 

 soil-moisture is in motion, the chances of aeration are 

 considerably better; thus at the edges of streams and 



