SECT. 11 



PHANEROGAM I A 



547 



Family 1. Betulaceae. — Male flowers adherent to the bracts; in catkins. 



Fig. ^17.— Alnns iiluUnosa. 1, Flowering branch bearing the small, erect female catkins and the 

 pendulous male catkins. 2, A bract-scale with male flowers. 3, Female catkins. U, Female 

 flower. 5, Catkin in fruiting condition. G, Fruit. {1 and the leaf, | nat. size ; 2-6, enlarged.) 



J. 



la. 



Female flowers in catkins. Ovary bilocular, witli two long stigmas ; a single 

 pendulous ovule in each loculus. Mainly distributed in the northern hemisphere. 



Most important Genera. — Alnus gliitinosa, the ^ 



Alder, is a prominent tree of damii Avoods, and is 

 also distributed in swamps and by the banks of 

 streams (Fig. 517). The leaves are bluntly obovate. 

 The inflorescences are already evident in the autumn 

 as stalked catkins, the male long and pendulous, the 

 female erect and short. Male flowers P4, A4 ; a 

 dichasium of three flowers adherent to each bract 

 (Fig. 518). The female flowers are in pairs, their 

 bracteoles adhering to the bract to form the five- 

 lobed, persistent, woody scale of the cone. Alnus 

 incana is distinguished by its leaves being grey and 

 hairy below. Bctula verrvxosa (Fig. 519), the Birch, 

 has a white bark and long-stalked, triangular leaves. 

 When young, all the parts are covered with numerous 

 glandular hairs which give the plant an aromatic, 

 resinous odour. The male inflorescences are formed 

 in the autumn of the previous year, singly or a few together, at the tip of shoots 



2 N 1 



Fio. 018. — Alnus (jlutinom. Dia- 

 grams of Fig. 517, Sand i. Bract 

 6 ; bracteoles a /3, a /3', a, |3,. 

 (After EiCHLEK.) 



