RHIZOMES AND ROOTS. 



(108) Sweet Flag Rhizome. 



The rhizome of Acorus Calamus, Linn. (N.O. Aroideae). 

 The rhizome presents the following structure : 



(1) Epidermis, consisting of a single row of cells covered by a 

 rather thick cuticle. In transverse section these cells appear 

 square, but in surface section they are axially elongated. 



(2) Cortex, of which the layers abutting on the epidermis are 

 collenchymatous and contain chlorophyll. The collenchy- 

 matous tissue passes into a dense parenchyma and this again into 

 a spongy parenchyma, the air-spaces in which are large and 

 separated from one another by a single layer of polygonal or 

 rounded slightly pitted cells containing minute grains of 

 starch. In this tissue there are numerous oil-cells commonly 

 situated at the point of intersection of the rows of cells. 



The cortex is traversed longitudinally by a number of fibro- 

 vascular bundles which are often accompanied by prismatic 

 crystals of calcium oxalate in the cells abutting on the 

 sclerenchymatous fibres. 



(3) Endodermis, consisting of a single row of quadrilateral cells. 



(4) Stele, similar in structure to the cortex. The wood of the 

 fibrovascular bundles consists of spiral, reticulated and scalari- 

 forna vessels ; there is a distinct sheath of fibres with thickened 

 pitted walls. 



The diagnostic characters of powdered sweet flag rhizome 

 are : 



(a) The abundant thin-walled parenchyma. 



(b) The very numerous minute starch grains. 



(c) The numerous oil cells. 



(d) The paucity of fibres. 



(e) The numerous scalar if orm vessels. 



