RADIX RHEI. RHUBARB. Ill 



lar, lo to 25 cm. long, nearly 0.5 cm. thick, with a 

 swollen warty crown, produced by the remnants of 30 to 

 40 stems, with reddish scaly leaves. A few tortuous, 

 irregularly contorted branches are given off, generally at 

 right angles. Just below the crown the root is zigzag 

 in outline, twisted about a keel, and sometimes transversely 

 wrinkled. The keel and wrinkles are more prominent 

 in the dry condition. The color of the root is yellowish- 

 gray to brownish-yellow, white within, the fracture sharp 

 and short, the odor and taste acrid. 



Histology. — The cortex is light brown, surrounded by a 

 dark periderm, the xylem cylinder white and crossed by 

 narrow medullary rays. Further down, where the keel is 

 well developed, the wood is defective and parenchyma is 

 substituted for it in many places. 



Under the microscope the periderm consists of layers 

 of cork tissue. The primary cortex is made up of thin- 

 walled parenchyma cells, which fill out the woody portion 

 where this is defective. Within the keel the inner cortex 

 is well developed and made up of several rows of medul- 

 lary rays and of bast- fibres. The wood is penetrated by 

 more narrow medullary rays, which resemble those of the 

 inner cortex. The xylem bundles contain wide vessels 

 and the parenchyma cells of the primary and secondary 

 cortex are filled with oil droplets and a pale yellow sub- 

 stance which dissolves in potassium hydrate. 



Chemistry. — The chief ingredients are senegin, fatty 

 and ethereal oil, volatile fatty acid, mucilage, tannin, 

 sugar and pectin. 



RADIX RHEI. RHUBARB. 



Rhubarb is the root of Runtex officinale, an herbaceous 

 perennial, growing indigenously in the eastern Asiatic 

 countries. The best specimens are the so-called Chinese. 



Description. — In cylindrical or flattened segments de- 

 prived of the brown corky layer, covered with a 



