210 RHIZOMES AND ROOTS. 



SECTION VIII. 



POWDERED RHIZOMES AND ROOTS, 



Rhizomes and roots often exhibit great similarity in appear- 

 ance as well as in structure. Some drugs consist of rhizomes 

 with roots attached to them (valerian), others of separate 

 pieces of rhizome and root which, however, are often with 

 difficulty to be distinguished (liquorice), whilst others, again, 

 though generally styled roots, are really rhizomes (rhubarb). 

 For these reasons it is desirable to deal with them together, 

 although such a classification may not be altogether scientific. 

 Most of such as are used in pharmacy are derived from mono- 

 cotyledonous or dicotyledonous plants, only one viz., male fern 

 being obtained from a fern. As the general structure varies 

 according to the class to which the plant yielding the drug 

 belongs, these classes may be considered separately. 



1. Ferns. 



The epidermis is succeeded by a tegumentary tissue consisting 

 of the suberised and dark-coloured outer rows of the cells of the 

 cortical parenchyma (metaderm). The steles are arranged in a 

 diffuse ring and surrounded by a parenchymatous tissue that is 

 continuous with, and may be considered part of the cortical 

 parenchyma, the cells of which contain small starch grains, 

 chlorophyll, etc. Each stele is surrounded by a distinct eiido- 

 dermis within which there is a single row of pericyclic cells 

 containing starch grains. Within the pericycle is a ring of bast 

 tissue, the centre of the stele being occupied by the wood. 

 The bast tissue is composed of small parenchymatous cells and 

 large sieve tubes, while the wood contains narrow spiral, together 

 "with larger scalariform and reticulate, vessels. 



