RHUBARB 



363 



which the alternating white and dark red lines alluded to can be seen. 

 The dark lines are medullary rays containing brown colouring matter ; 

 the white lines consist of bast parenchyma containing starch and 

 calcium oxalate. Occasionally minute dark points or projections may 

 be detected which, when carefully shaved off with a knife, exhibit 

 radiating red and white lines ; these are the remains of fibro- vascular 

 bundles from the leaves (leaf-traces) and pass through the bark into 

 the central portion of the rhizome. 



The drug is firm, heavy, and compact, the outer surface showing 

 little sign of shrinkage during the drying ; it breaks with an uneven 

 fracture, the fractured surface, which varies from bright pink to dull 



FIG. 189. Chinese Rhubarb (Shensi flat). Transverse section, showing 

 the remains of the bark (as a narrow exterior layer), the cambium (as 

 a dark line), the wood (with a more or less distinctly radiate structure), 

 and an irregular circle of starspots (abnormal fibro -vascular bundles). 

 (Planchon and Collin.) 



grey in colour, exhibiting under the lens dark reddish brown lines 

 alternating with white ones (' nutmeg ' fracture). The transverse 

 section shows near the periphery a more or less continuous ring of large, 

 conspicuous, star-like spots, each of which consists of dark red lines 

 (medullary rays) radiating from a common centre through a white 

 groundwork (parenchyma). These star-spots are fibro- vascular bundles 

 which also traverse the inner part of the drug in varying directions. 

 Exterior to this ring the drug exhibits a radiate appearance due to the 

 formation of a narrow ring of secondary w r ood by the cambium, which 

 is sometimes evident as a dark line about 1 mm. from the margin 

 (compare fig. 189), but is often not seen, as not only the whole of the 

 bark but even part of the secondary wood may have been removed by 

 the peeling. If the peeling has been sufficiently deep to remove the 

 bark and the secondary wood as well, then the star-spots appear on 

 the outer surface, but until then they are indistinct. They can always 

 be seen on the flat (inner) surface of the plano-convex pieces. Beyond 



