284 COMMON TREES AND SHRUBS 



Birch (Betula tomentosa) is the most abundant. Its branches 

 are greyish-brown, slender, but seldom droop, and the 

 fresh young twigs are hairy. The Silver Birch [Betula 

 alba) is a more elegant tree and is not so common. The 

 branches are long and slender and often droop gracefully. 

 Its young twigs are covered with resinous warts. 



The buds are ovoid and covered with stipular scales, and 

 the same gradation is met with as in the Hazel. The 

 leaves are alternate, scattered and small ; the base is small 

 and leaves a small scar ; the stalk is slender and the blade 

 variable. Usually it is broadly ovate to cordate, with 

 a doubly serrate margin, and the surface is glabrous with 

 prominent veins beneath. 



The Birch is a tree of fresh air and sunshine. It has a 

 very open canopy, its small scattered leaves (Fig. 188, 2) 

 do not form mosaics, and neither shade each other nor cast 

 much shade on the ground. It grows badly under the 

 shadow of other trees, and is thereforecalled a light-dem and- 

 ing tree. Usually the undergrowth is equally light- 

 demanding. 



The male and female flowers are in separate catkins on 

 the same tree (monoecious). The male catkins are deve- 

 loped in the autumn, and are seen on the trees throughout 

 the winter, two or three together at the ends of the twigs 

 (Fig. 188, 1 m.c). In the spring, as the leaves come out, the 

 catkins elongate, droop, and shed an abundance of pollen. 

 The flowers are arranged on the catkin in three-flowered 

 cymes (3 and 4). On the upper side of each bract are two 

 smaller bracts (3 br) ; then three flowers, each with two 

 split stamens, which thus resemble four stamens. 



The female catkins are enclosed in buds during the winter, 

 but in February they begin to open (1 f.c). At the base 

 three or four leaves form on dwarf shoots, and each shoot 

 ends in a slender catkin. As in the male catkin the flowers 

 are in threes (4). Each bract has two small scales above it 



