268 RHIZOMES AND ROOTS. 



(129) Valerian Rhizome. 



The rhizome and roots of Valeriana qfficinalis, Linn. (N.O. 

 Valerianese). 



The rhizome presents the following structure : 



(1) Tegumentary tissue, composed of large polygonal cells 

 which are slightly suberised. 



(2) Cortex, the cells of which are rounded or oval, exhibit inter- 

 cellular spaces, and are filled with starch. 



(3) Endodermis, consisting of a single layer of tangentially 

 elongated cells containing volatile oil. 



(4) Stele, in which a pericycle and a bast ring surround a circle 

 of wood-bundles within which there is a very large pith. The 

 T ericycle is narrow, the bast parenchyma is collenchymatous and 

 in the pith there are scattered groups of sclerenchymatous cells 

 with thickened pitted walls. 



The structure of the root is as follows : 



(1) Epidermis, the cells of which are rectangular in tangential 

 section and axially elongated. 



(2) Hypoderma, consisting of large cells containing volatile 

 oil. 



(3) Cortex, which is comparatively wide and contains in its 

 cells an abundance of starch in simple or small compound 

 grains; the innermost row of cells (endodermis) contains 

 volatile oil. 



(4) Stele, in which the wood bundles form an almost con- 

 tinuous ring enclosing a large pith, the cells of which also 

 contain starch. The pith of the root does not contain 

 sclerenchymatous cells as that of the rhizome does. 



The diagnostic characters of powdered valerian rhizome and 

 roots are : 



(a) The cells containing volatile oil. 



(b) The abundant starch. 



(c) The epidermis of the root, with hairs. 



(d) The sclerenchymatous cells. 



