246 The Birches 



The genus comprises about 7 species, mostly shrubs, indigenous to the northern 

 hemisphere; two of them are well-known shrubs of the north and eastern United 

 States. The popular Filbert of commerce is the nut of the European Hazelnut, 

 Corylus Avellana Linnaeus, the type of the genus, and cultivated in a number of 

 improved varieties; over a dozen fossil species of the genus have been described. 

 The name is Greek in reference to the helmet-like involucre surrounding the nut. 



IV. THE BIRCHES 



GENUS BETULA [TOURNEFORT] LINNAEUS 



[[BOUT 35 species of birches are known, some 25 of them trees, the others 

 shrubs. They are widely distributed throughout the north temperate 

 and subarctic zones, some of the shrubby kinds extending as far north- 

 ward as any woody plants. In North America, besides the fifteen trees 

 here described, there are four or five kinds of shrubs. Betula is the ancient Latin 

 name; B. alba Linnaeus, the European White birch, is the type of the genus. 



The bark and wood contain an aromatic volatile oil. The wood is close- 

 grained, hard, and tough, that of all the birch trees being good fuel. The leaves 

 are variously toothed, rarely lobed or incised, and are stalked, pinnately veined, 

 and stipulate, the small stipules falling away as the leaves imfold in spring. The 

 minute monoecious flowers are in dense catkins, opening in very early spring, before 

 or as the leaves unfold. The staminate catkins at flowering time are long and 

 drooping, the pistillate ones shorter, upright or spreading. The staminate flowers 

 are borne at the bases of the scales of the catkin and consist of a 4 -toothed or 

 2 -toothed calyx and 2 stamens with short, 2 -forked anthers, each fork bearing 

 an anther-sac. The pistillate flowers are usually 2 or 3 together at the base of 

 each scale of the catkin; they consist only of a 2-celled ovary, surmounted by 2 

 long styles stigmatic near the tip. The ripe pistillate catkins (strobiles) consist of 

 the leathery 3-lobed scales, bearing the minute flat membranous- winged nuts, and 

 these fall away together from the slender axis. 



Fruiting catkins slender-stalked. 

 Bark of the trunk chalky white (rarely darker in B. papyrifera). 

 Leaves deltoid or rhombic. 



Leaves long-acuminate; eastern trees. 



Leaves bright green, shining, irregularly toothed. 1. B. poptdijolia. 



Leaves dull blue-green, regularly toothed. 2. B. casrulea. 



Leaves short-acuminate; northwestern tree. 3. B. alaskana. 



Leaves ovate; strobile-scales not hairy-fringed. 

 Leaves rounded or narrowed at the base. 4. B. papyrifera. 



Leaves cordate at the base. 5. B. cordijolia. 



Bark of the tnmk brown to red-brown or green-brown. 

 Leaves ovate to ovate-orbicular; western trees. 

 Tall trees with incised-serrate leaves. 



Leaves rounded at the base, finely serrate. 6. B. occidentalis. 



