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 externall}- ; whitish internally ; the 

 bark is thick, wood with about 12 fibrovascular 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. enropaum 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^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 endo- 

 sperm is mealy. 



Rheum ofUcinale is the source of the " South China " rhubarb 

 from Szetschuan (p. 474). The plant is a perennial herb resem- 

 bling the garden rhubarb (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 re- 

 lated species which also yield the drug. Rheum pahnatum of 

 Northern China has leaves which are lobed or deeply incised, 

 which character is especially marked in the variety tanguticum. 

 Rhemn Rhaponticum, 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 cultivation in botanical gardens in Europe. 



Rumex crispus or curled dock is a perennial herb growing in 

 fields and waste places in the P^nited States and parts of Canada. 

 The leaves are oblong-lanceolate, with an undulate margin 



