TREES AND SHRUBS. 395 



hang vertically on the drooping twigs, they cast little shade. 

 Hence the Birch catches but little light, as compared with 

 trees which spread out their leaves and form a mosaic. It 

 is, in fact, the most exacting tree in its demand for light, and 

 conversely it grows worse in shaded places than any other 

 tree in Britain. 



Between an extreme light-demanding tree like the Birch 

 and an extreme shade- enduring tree like the Beech we get 

 various intermediate trees. The buds are small, pointed, 

 dark brown; some produce long shoots, others dwarf shoots. 

 Each year the end of the long shoot dies and its growth is 

 continued by the uppermost side bud. 



The catkins open along with the leaves in March or April 

 (Fig. 161). Both kinds are cylindrical; the female catkins 

 are at first erect and more slender than the male catkins, but 

 later (in fruit) become much larger. The male catkins are 

 visible during autumn and winter (as in Hazel) at the ends 

 of twigs in twos or threes. 

 In spring the male catkin 

 lengthens and droops, the 

 scales separate, and the pollen 



is blown out. Each scale ^OH-lffe^ BRACT 

 (bract) bears (on its true 

 upper surface) several small 

 scales and three groups of 

 stamens, each group consist- BRACT EO LE 

 ing or two stamens each split 

 into two half-stamens (Fig. Fig. i62.-Bi.-ch. 



-,nf) \ A Female flowers in axil of bract; B, 



1O4, C). Fruiting scale, with tliree samaras; 



Each female Catkin is pro- C ' stamen from male flower. 



duced inside a resting-bud ; in 



spring this bud grows out, produce? a few foliage-leaves, 

 and ends in a slender catkin (Fig. 161). Each scale bears 

 on its upper side two small scales (bracteoles, Fig. 162, A) 

 and three flowers. Each flower consists of a pistil (like that 

 of Hazel in structure), without any cup. The akene is flat 

 and produced at each side into a thin wing. In autumn the 

 scales fall off and the light- winged fruits are dispersed by 

 the wind. 



Examine twigs in autumn, noting the ripe female catkins 

 of this year, and the male catkins and the buds for next 



