498 POLYGONACE^. 



portions of a massive root which display considerable diversity of form, 

 arising from the various operations of paring, slicing and trimming, to 

 which they have been subjected. Thus some pieces are cylindrical or 

 rather barrel-shaped, others conical, while a large proportion are plano- 

 convex, and others again are of no regular shape. These forms are not 

 all found in the same package, the drug being usually sorted into round 

 and Jiat rhubarb. In dimensions we find 3 to 4 inches the commonest 

 length, though an occasional piece 6 inches long or more may be met 

 with. The width may be stated at 2 to 3 inches. The outer surface of 

 the root is somewhat shrivelled, often exhibiting portions of a dark bark 

 that have not been pared away. Many pieces are pierced with a hole, 

 in which may be found the remains of a cord used to suspend the root 

 while drying. The drug is dusted over with a bright brownish-yellow 

 powder, on removal of which the outer side of the root is seen to 

 have a rusty -brown hue, or viewed with a lens to be marked by the 

 medullary rays, which appear as an infinity of short broken lines of 

 deep brown, traversing a white ground. 



The character which most readily distinguishes the rhubarb of China 

 is that well-developed pieces, broken transversely, display these dark 

 lines arranged as an internal ring of star-like sjwts. Although this 

 character is by no means obvious in every piece of Chinese rhubarb, it 

 is of some utility from the fact that in European rhubarb, such spots 

 are generally wholly wanting, or at most occur only sparingly and in an 

 isolated manner. 



In judging of rhubarb, great stress is laid upon the appearance of 

 the root when broken, and the circumstance of the fractured surface 

 presenting no symptoms of decay, discoloration, or sponginess.^ In good 

 rhubcirb, the interior is found to be compact, and beautifully veined with 

 reddish-brown and white, sometimes not unmixed with iron-grey. The 

 root when chewed tastes gritty, by reason of the crystals it contains of 

 oxalate of calcium ; but it is besides bitter, astringent and nauseous. 

 The odour is peculiar, and except by the druggist, is mostly regarded 

 as very disagreeable. 



Microscopic Structure. — The tissue of rhubarb is made up of a 

 white parenchyme, brown medullary rays and a few irregularly scattered 

 very large fibro- vascular bundles, which are devoid of ligneous cells. 



On a transverse fracture of specimens, which are not too much peeled, 

 a narrow dark cambial zone may be distinguished. In that part of the 

 root, only the medullary rays display the usual radial arrangement, and 

 in the interior of the root no regular structure is met with. There is no 

 well-marked pith, but the central portion of the tissue shows a mixture 

 of white parenchyme and brown medullary rays running in every direc- 

 tion. In full-grown roots, the central part is separated from the cambial 

 zone by the band of stellate patches" already mentioned. 



^ The quality and appearance of rhubarb ^ Their formation has been investigated 



are far more regarded in England than on by Schnaitz, Proceedings of the " JVafur- 



the Continent. To ensure a fine powder of forschende Gesellsdiaft zu /Julie "; theauthor 



brilliant hue, the drug is most carefully pre- also shows that the drug is chiefly afibrded 



pared, each root being split open, and any by the rhizome. — An abstract of the paper 



dark or decayed portion removed with a will be found in Just's Botaniacher Jahres- 



chiselorfile, whiletheoperatorisnotallowed het-icht, 1874. 4G1. 

 to handle the drug except with leather 

 gloves. 



