520 A TEXT-BOOK OF BOTANY. 



official drug serpentaria (see Vol. II). From a slender rhizome 

 with numerous hair-like roots arise one or more short, leafy 

 branches which are more or less simple, somewhat hairy, and bear 

 oblong-cordate, prominent-reticulate, hairy leaves (Fig. 287). The 

 flowers are borne on slender, scaly, basal branches ; the calyx tube 

 is purplish and curved like the letter " s," being enlarged around 

 the ovary and at its throat. The fruit is a capsule containing 

 numerous flat or concave seeds. An allied species, Aristolochia 

 Serpentaria, furnishes the drug Virginia snakeroot. .It is a more 

 delicate plant, the leaves being ovate-lanceolate, acuminate; the 

 flowers are solitary, and in some cases cleistogamous. This species 

 is found growing in the United States, more especially east 

 of the Mississippi, while Aristolochia reticulata is found west 

 of the Mississippi from Arkansas to Texas. The plants of this 

 genus contain volatile oils, and in addition to the two species 

 mentioned 45 other species are used in medicine in various parts 

 of the world. 



Asarum canadense (Canada snakeroot or wild ginger) is a 

 plant common in the Northern United States and Canada (Fig. 

 288). The long and slender rhizomes are used in medicine. 

 They are 5 to 15 cm. long, about 2 mm. thick, more or less bent 

 and curved, purplish-brown externally ; whitish internally ; the 

 bark is thick, wood with about 12 fibre vascular bundles, pith large ; 

 the odor is aromatic ; the taste pungent and bitter. The drug con- 

 tains 2 to 3 per cent, of a volatile oil containing a fragrant body, 

 asarol ; a pungent, fragrant resin ; a yellow coloring principle 

 which is colored dark green with ferric salts ; and starch. The 

 volatile oil obtained from A. europccum contains a principle (asa- 

 rone) which forms irritating vapors on heating. 



X. ORDER POLYGONALES. 



This order is represented by a single family, the POLYGONACE.E 

 or Buckwheat family. The plants are mostly herbs, but include 

 some twining vines and shrubs. The leaves are simple, mostly 

 entire, and characterized by having a stipulate appendage (ocrea) 

 which sheaths the stem. The flowers are small, perfect, and with 

 a 2- to 6-parted perianth. The fruit is a 3- to 4-angled akene. The 

 embryo is either straight or curved, and the endosperm is mealy. 



