218 RHIZOMES AND ROOTS. 



(104) Belladonna Root. 



The root of Atropa Bellaljnna,, Linn. (N.O. Solanacese). 



The upper part of the root is an erect rhizome and differs 

 somewhat from the root in its structure. 



A root of moderate size presents the following structure : 



(1) Cork, composed of tabular, tangentially elongated cells 

 which in surface view are polygonal and isodiametric. 



(2) Cortex (secondary), consisting of parenchyrnatous cells 

 with rather thick walls and distinct pits ; near the cork these 

 cells are tangentially elongated, but towards the cambium they 

 become nearly isodiametric. In the cells of this tissue, as well 

 as those of the parenchyma of the bast-ring and wood, starch 

 grains and sandy crystals of calcium oxalate occur. The starch 

 grains vary usually from 5 to 20//, in diameter, but may 

 attain 30/x, ; they are mostly compound and contain from two 

 to four constituent grains ; the simple grains are rounded 

 or oval. 



(3) Bast Ring, which is not sharply delineated from the cortex 

 and contains radially elongated groups of sieve-tissue, but no 

 bast fibres. 



(4) Wood, consisting largely of thin-walled parenchyma, 

 throughout which radially elongated vascular groups are distri- 

 buted, the centre of the root being occupied with the primary 

 wood. The vascular groups contain a few pitted vessels, 

 accompanied by tracheids and fibres. 



The rhizome differs considerably from the root in structure. 

 The wood is much more developed and usually forms one or more 

 dense rings enclosing a distinct pith, and traversed by well 

 marked medullary rays. Between the pith and the wood 

 perimedullary bast bundles may be found. 



The diagnostic characters of belladonna root are : 



(a) The starch. 



(b) The sandy calcium oxalate. 



(c) The characteristic tracheids and wood fibres. 



