TREES AND SHRUBS FURNISHING MEDICINAL BARKS. 



17 



Fig. 8. — Sweet birch (Bctuhi lenta), trunk. 



one-half inch, and has rough, platelike fissures (fig. 8). The younger hranches 

 are covered with a beautiful, shining, reddish brown bark, with a layer of 

 yellowish green beneath the surface, 

 and furnished with numerous small, 

 whitish spots, known technically as 

 " lenticels." and which may be desig- 

 nated as "breathing pores." In most 

 of the birches the bark comes off in 

 layers, but this is not the case with 

 the sweet birch. The youngest twigs 

 of the sweet birch are densely hairy. 

 The wood is much used in cabinet work, 

 being fine and close grained, and tak- 

 ing on a very high polish. It has a 

 rosy color when first cut, which be- 

 comes darker by exposure. 



The young leaves are covered with 

 shining, silvery, silky hairs, but as 

 they grow older these disappear almost 

 entirely. In shape the leaves are oval 

 or oblong-oval, acute or acuminate at 

 the apex, somewhat heart shaped at 

 the base, and sharply toothed; they 

 are about •"> to 4 inches long and 1 to 

 2 inches wide, smooth, bright green 

 and shining on the upper surface, 

 and dull green on the lower surface 



with hairy veins. (Fig. 9.) Like the bark, the leaves are also aromatic. 

 The flowers are of two kinds, staminate or male and pistillate or female, and 



are borne in separate catkins or slender 

 spikes. The male catkins are in droop- 

 ing clusters 2 to o inches long, while 

 the female catkins are shorter, only 

 about 1 inch or less in length, thicker, 

 stemless. and nearly erect. (Fig. 9.) 

 They expand with the leaves or be- 

 fore, about April or May. The cylin- 

 drical, conelike fruit is about an inch 

 in length. The sweet birch belongs 

 to the birch family (Betulacea?). 



Description of bark. — The birch 

 bark of commerce consists of pieces of 

 irregular size. generally reddish 

 brown and smooth on the outside, 

 the thin outer layer having been re- 

 moved, but with pieces of it some- 

 times adhering. The inner surface is 

 also reddish brown and smooth. 

 Birch bark breaks with a clean, even, 

 somewhat granular fracture. 



Collection, prices, and uses.— The 

 bark is collected in late summer. It 

 furnishes the oil of sweet birch or oil of P.etula. official in the United States Phar- 

 macopoeia, and obtained by maceration and distillation. It is almost identical 

 139 



Fig. 9. — Sweet birch (Betula lenta] 

 catkins, and fruit. 



leaves. 



