342 



DICOTYLEDONES. 



FIG. 325. Alnus glutinosa: A dichasium of cJ -flowers seen 

 from the front; B the same from inside ; C the same from the 

 back ; D dichasium of ? -flowers with subtending-leaf and four 

 bracteoles. The letters b, a, ft, ft', ft, are the same as in Fig. 

 326 A. 



324 ?>). Each cover-scale supports two winged or wingless nuts. 

 In the native species of Alder the buds are stalked (Fig. 324 k). The bud- 

 scales are formed by the stipules of the lowest leaves. 



Betula (Birch). The <$ -catkins, in the native species, appear in 

 autumn, the ? -catkins in the flowering year on leaf-bearing, short- 

 lived shoots. (J -flowers : 2 stamens, divided (Fig. 328.4). The 3- 



lobed cover-scales 

 (Fig. 327 a) of 

 the ? -catkin are 

 detached from 

 the axis ; each 

 cover-scale sup- 

 ports 3 broadly- 

 winged nuts (b). 

 The stem has cork 

 with annual rings. 

 The young twigs and 

 leaves have aromatic 

 resin glands. 



THE INFLORESCEN- 

 CES OF THE ALBEB. 

 In the axil of each 

 cover-scale [b in the Figs ] is situated, in the $ -catkins (Figs. 326 A, 325 A-C) 

 a 3-flowered dichasium, the flowers of which have a 4-partite perianth, the 

 posterior perianth-segments being sometimes almost suppressed, and 4 stamens 

 with undivided filaments. In the $ -catkin (Figs. 325 D, 326 C') a 2-flowered 



dichasium is found, the middle flower 

 being suppressed (indicated by a star in 

 C). In both instances the inflorescences 

 have two bracteoles (a-/i) and the 

 flowers borne in their axils have each 

 one bracteole (/3'), the other one (a') be- 

 ing suppressed and therefore in 326 A 

 and C only represented by a dotted 

 line ; these four bracteoles unite with 

 the cover-scale (b) which supports the 

 entire dichasium, to form the 5-lobed 

 " cone-scale " (Fig. 326 B) which in the 

 $ -catkin eventually becomes woody. 



THE INFLORESCENCES OF THE BIRCH. 

 A 3-flowered dichasium is situated in 

 the axil of the cover-scale in both (?- 

 and ? -catkins (Fig. 328 .4, B) ; only the 

 central flower has bracteoles (a-j3) (the 

 lateral flowers having no bracteoles), and these bracteoles unite, as in the Alder, 

 with the supporting cover-scale (b), and form a three-lobed cone-scale (Fig. 327 a). 



B 



FIG. 326. Alnus glutinosa: diagram 

 of dichasia of $ (A) and ? (C) catkins; 

 B a cone-scale. All the bracteoles in A 

 and C are slightly pressed from their 

 normal position. 



