394 



TREES AND SHRUBS. 



After fertilisation the ovary grows into a dry akene ; the 

 scales become stalked, hard, and woody, giving the old female 

 catkin the appearance of a Pine cone. The cone ripens in 

 autumn, but remains closed until the following spring, when 

 the scales become separated and the akenes (which have a 

 spongy coat) may be blown away by the wind or may fall 

 into wa.ter and be carried by it. 



386. Birch (Betula alba} is easily recognised by its thin 

 main stem (sometimes forty feet high), which runs up to the 

 top of the tree and is rarely over a foot in diameter; its 



slender twigs, drooping at 

 the ends, and the light 

 foliage, which together 

 give the tree its graceful 

 appearance ; and its 

 smooth thin white papery 

 bark with long, dark 

 transverse lenticels. 



There are two varieties 

 in Britain, " White " 

 Birch and " Common " 

 Birch; they are con- 

 nected by variations and 

 hybrids, but the " Com- 

 mon" Birch is distin- 

 guished by its branches 

 being more spreading and 

 rarely drooping at the 

 ends, its twigs not being 

 covered with hairs, its 

 bark being, at the base of 

 the trunk, rough, dark, 

 and furrowed, and by its hairless and longer-tipped leaves 

 with the blade placed horizontally. The young bark is 

 brown in both cases, becoming white later on. 



The leaves are arranged all round the stem, but sometimes 

 tend to form two rows ; the stalk is thin, the blade variable 

 in outline (heart-shaped, diamond- shaped, etc.), doubly 

 toothed, with pointed tip. Since the leaves are relatively 

 small, well spaced on the slender twigs, long-stalked, and 



Fig. 161. Birch. Twig showing male and 

 female catkins. 



