46 SHADE AND BRANCHING [CH. 



No physiological observation is better established than 

 that any foliage-shoot which persistently throws a deep 

 shadow on another similar shoot, at once places the latter 

 at an enormous disadvantage in the struggle for existence. 

 The sufficiently illuminated and aerated shoot dominates 

 the over-shaded one, and it is only a matter of time how 

 long the latter can hold out at the expense of the supplies 

 stored up in its tissues. 



Two very direct consequences of the competition of 

 shoots for light are seen in the paucity of foliage or even 

 total lack of leaves in the interior of the crown of a tree, 

 and in the "cleaning of the bole," as foresters term it, 

 when the stem is sufficiently over-shadowed by its own 

 foliage or by that of other trees. Different trees differ 

 considerably in the amount of shade they will beai-, or, 

 what amounts to the same thing, in the degree of intensity 

 of light which suits them best. For instance, the Birch, 

 with its sparse foliage on relatively few branches, stands 

 in marked contrast to the Beech with its densely foliaged 

 and crowded branches. The formei- casts a very feeble 

 shade in which numerous flickers of sunlight play, and 

 almost any tree can withstand its shadow, whereas it is 

 itself very intolerant of shade. The Beech on the other 

 hand casts a dense dark and cool shade, beneath which 

 scarcely any plant can grow, and is itself capable of 

 enduring for a long time the shadows of most other trees. 

 Similarly with the Larch and the Yew, the former of 

 which casts the lightest and least sustained of shadows 

 among Conifers, partly owing to the loose and open 

 arrangement of its foliage and partly because, being de- 

 ciduous, it is devoid of leaves from November to April or 

 even longer, whereas the Yew is evergreen and casts a 

 deep shade owing to its evergreen and densely crowded 

 foliage. 



