AMENTACEiE 



375 



in groups of three, on the scales of the cone-like fruit. 

 Each of the hardened cone-scales is formed by the union 

 of the three bracts which subtend the group of female 

 flowers (see Figs. 295, 296). We have two species — the 

 Common Birch, a tree with pointed leaves {B. alba) ; 

 and B. nana, a shrub with small orbicular leaves (see 

 Viola palustris, p. 28). The colouring is rich and 

 varied : the stems white and black, boughs coppery, 



Fig. 295.— Cone -scale of Birch, 

 formed by union of the bract 

 B, and the pair of bracteoles, 

 a, b. Much enlarged. See 

 next figure. 



Fig. 296. — Diagram of a three-fiowered group 

 from the female catkin of Birch. A , posi- 

 tion of axis of catkin ; ^, bract .subtending 

 the group of ilowers ; a, b, bracteoles ; 

 1, median ; 2 and 3, lateral flowers. 



twigs purple, and leaves green or gold according to 

 the variety and the season of year. The pleasant 

 smell of Eussian leather is said to be given by an oil 

 distilled from the Common Birch. 



Carpinus (Hornbeam) 



Monoecious wind flowers ; males with about 12 

 stamens. The fruit is small, one-seeded, and very hard, 

 attached to a long, leafy, unequally three-lobed bract, 

 so that it is easily carried by wind. 



0. Betulus. — A group of two flowers is borne in the 

 axil of each bract of the female catkin (Figs. 297, 298). 

 This group of two is comparable with the three-flowered 

 group in Birch, the central flower being suppressed. 

 The main bract B, subtending the group, plays no part 

 in the formation of the cupule ; the pair of three-lobed 



