262 BOTANY AND PHARMACOGNOSY. 



78, B). 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 fibrovascular bundles, pith large; 

 the odor is arornatic ; 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 Polygon- 

 ace^ 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 she&ths the stem. The flowers are small, perfect 

 and with a 2- to 6-parted perianth. The fruit is a 3- to 4-ang!ed 

 akene. The embryo is either straight or curved, and the endo- 

 sperm is mealy. 



Rheum officinale is the source of Chinese rhubarb (p. 474). 

 The plant is a perennial herb resembling the common garden 

 rhubarb or pieplant (Fig. 205). The rhizome is vertical and 

 gives rise to a leafy branch terminated by the inflorescence which 

 is a panicle. The leaves are large, with a sub-cylindrical petiole, 

 a cordate or orbicular lamina which is either entire or coarsely 

 and irregularly dentate. There are several nearly related species 

 which also yield the drug. Rheiiui palmatum of Western China 

 has leaves which are lobed or deeply incised, which character is 

 especially marked in the variety tanguticum. Rheum Rhaponti- 

 cnm, which yields English rhubarb, has leaves which are heart- 

 shaped at the base and with a more or less irregularly undulate 

 margin. All of these species are more or less common in culti- 

 vation in botanical gardens in Europe. 



Rumex crispus or curled dock is a perennial herb growing in 

 fields and waste places in the United States and Canada (Fig. 

 138). The leaves are oblong-lanceolate, with an undulate margin 



