BETULACEAE. 



23 



BETULA. Birch. 

 (Family Betulaceae). 



Trees or less commonly shrubs: 

 deciduous. Twigs slender, usu- 

 ally zig-zag, terete, frequently de- 

 veloping as dwarf-shoots so as 

 to make the lateral buds appear 

 stalked: pith minute, compressed 

 3-sided, continuous, green. Buds 

 moderate, solitary, fusiform -ovoid, 

 sessile, with 2 or 3 exposed scales, 

 the end-bud usually deciduous ex- 

 cept on the numerous short spurs. 

 Leaf-scars alternate, more or less 

 2-ranked, half-elliptical, small: 

 bundle-traces 3, sometimes indis- 

 tinct: stipule-scars narrow. 



Though they have been much 

 confused in botanical publications, 

 the birches are not very difficult 

 as a rule. In accordance with the 

 policy of adhering to the nomen- 

 clature of the Standard Cyclope- 

 dia of Horticulture, the names here used are somewhat differ- 

 ent from those employed in the last edition of Gray's Manual, 

 though the latter rest on an extended critical study of the 

 group by Fernald, published in full in The American Journal 

 of Science for September, 1902. 



An excellent character is derived from the bracts of the 

 fruiting cones, which are sometimes available in winter; and 

 this character has been applied successfully to the recognition 

 of certain hybrid birches by Rosendahl in volume four of 

 Minnesota Botanical Studies. 



