CHAPTER XXIII: THE BIRCHES 



Family Betulace.^ 



Genus BETULA, Linn. 



Trees with smooth bark marked with conspicuous horizontal 

 sHts {leniicels), usually curling back in thin horizontal layers. 

 Leaves simple, alternate, deciduous, serrate, stalked. Flowers 

 monoecious, in catkins. Fruit cone-like, scaly; seed flat, winged. 



KEY TO SPECIES 



A. Bark chalky white, yellow beneath. 

 B. Leaves triangular, bark close. 



{B. pOpulifolid) WHITE BIRCH 



BB. Leaves ovate; bark separating freely into layers. 



(B. papyrifera) canoe birch 

 AA. Bark grey, curling back, yellow beneath. 



(B. luted) yellow birch 

 AAA. Bark red, curling in thin ribbons; cones ripe in June. 



{B. nigra) red birch 

 AAAA. Bark dark brown, lustrous. 



B. Twigs aromatic; bark separating into thick plates. 



{B. lenia) sweet birch 

 BB. Twigs not aromatic; bark separating into thin, papery 



layers. (B. occidentalis) western black birch 



There is no denying the inferiority of the wood in most species 

 of birch. The toughness and durability of the bark prevent the 

 prompt evaporation of the abundant sap, which ferments and 

 breaks down the wood cells. It is not uncommon to find in the 

 woods a birch trunk with the bark intact, but the wood crumbling 

 like chalk when touched. When the trees are stripped of their 

 bark immediately after being cut down, the wood seasons properly 

 and lasts fairly well as lumber. 



There are twenty-eight known species of the genus Betula 

 distributed over the Northern Hemisphere, and a fugitive species 



1O7 



