BIRCH 233 



end of long shoots 4 5 cm. long; both 

 cylindroid and pendent. Scales tri-lobed, 

 composed of the fused bracteoles and bract. 

 Catkin- scales small and closely imbricated, 

 each bearing in its axil a small group of 

 3 flowers with bracteoles ; the <$ flowers 

 with free stamens and a perianth (mono- 

 chlamydeous), the $ naked (achlamy- 

 deous) ; fruit a winged samara. 



Betula alba, L. Birch (Figs. 72, 73). Tree with 

 monoecious anemophilous flowers, the </ in pendent 

 catkins; pendent long thin branches, and white peri- 

 derm ; leaves more or less triangular-ovate and distichous. 



Catkins cylindroid, pendent ; the </ about 3 6 x 0*6 

 0'8 cm., with brownish scales and yellow anthers ; the 

 $ about 1 2 x 0'2 cm., olive or yellowish, with purple 

 stigmas, but growing larger (up to 4 8 cm. or more) as 

 the fruits ripen. Scales 3-lobed i.e. of the cover-scale and 

 two adherent bracteoles deciduous with the fruits. 



The catkin is more complex than in Salix and Populus, 

 where each scale carries only one naked flower; here 

 the scale subtends a small inflorescence (dichasium), in 

 each case a dichasial cyme of three flowers with their 

 bracteoles, which latter fuse with the deciduous catkin- 

 scale, and give to it the compound 3 5-lobed character 

 observed on dissection. Scales red -brown, ciliate ; stamens 

 yellow, anthers glabrous. 



Each ff flower consists of about two minute bract- 

 like perianth segments, enclosing two branched furcate 

 stamens ; each $ flower consists of a naked flattened ovary 

 with 2 cells, 2 ovules, and 2 stigmas, but ripens to a 

 winged achene. The $ catkins, 10 40 up to 60 90 mm. 

 long, terminate the dwarf shoots ; the </*, at the end of the 

 long shoots, pale green, with hairy stalk and ciliate scales. 



