CHAP, in.] Characteristics of Trees 57 



to assume their normal shape has only free scope when the 

 individual trees are growing in full exposure to light and air. 

 Those in which the leading-shoot develops more vigorously than 

 the side-shoots then assume a conical form ; whilst others, 

 whose side-shoots compete on anything like equal terms with 

 the axial shoot, remain short and stunted, and have low wide- 

 spreading crowns. The true characteristics of any tree are best 

 observable when it is grown in the open ; but, when the growing- 

 space allotted to each tree is limited, these natural tendencies are 

 checked, and a struggle upwards for individual exposure to 

 light and air ensues, which transforms the whole vital energy 

 into activity of growth upwards. This impulse is greatest in light- 

 demanding trees, and, within reasonable limits, may be said to 

 vary inversely to the growing-space allowed. Even when grown 

 in the open, Spruces, Douglas Fir, and Silver Firs, Larch, and 

 Weymouth Pine retain a distinctly noticeable central axis, which 

 is yet traceable, though less clearly, in Scots, Corsican, and 

 Austrian Pines, Alder, Beech, and sessile Oak, and to a still less 

 degree also in Ash, Maple, Sycamore, and Elm ; whilst on the 

 other hand the pedunculate Oak and Hornbeam have a marked 

 tendency to ramification and to the formation of a diffuse crown 

 at no great height above the ground. In woodland crops of 

 normal density the leafy crowns of Larch, Pines, Oak, Birch 

 and Aspen reach only a little way down the stem ; those of 

 Spruce, Douglas Fir, Beech and Hornbeam descend for about 

 one-third of the bole ; whilst in Silver Fir they often extend 

 almost half-way down. The effect of the concentration of the 

 crown of leafy foliage towards the summits of the stems ensures 

 the conservation pf the assimilated nourishment for the forma- 

 tion of long, straight, full-wooded stems of the highest possible 

 technical and financial value, in place of this being dissipated 

 over a large branch-system and a stunted stem. That such timber 

 must be more full-wooded, i.e. that the relative proportion 

 between the upper girth or diameter and the lower should 

 show less difference, is easily intelligible, owing to the larger 



