212 RHIZOMES AND ROOTS. 



is the case with most drugs, and it is often anything but an 

 easy task to distinguish the one from the other. Rhizomes, 

 however, generally possess a well-marked pith which is absent 

 from roots, and they often exhibit also scars of leaves with 

 buds in their axils from which roots are free ; in transverse sec- 

 tion it is usually easy to discover the leaf traces that proceed 

 from the stele obliquely through the cortex to these leaves. 



Principal Tissues of Roots and Rhizomes. 



Before reviewing the principal tissues that are present in roots 

 and rhizomes it may be observed that hairs, both simple and glan- 

 dular, stomata and palisade tissue, all of which are commonly 

 present in leaves, are almost wholly absent from roots and rhi- 

 zomes and their powders. The sclerenchymatous and coloured 

 layers that are characteristic of seeds are not found in roots, 

 which may also be distinguished from seeds by the absence of aleu- 

 rone grains. The presence of pitted and other vessels are sufficient 

 to distinguish powdered roots from powdered barks, with the 

 exception of those few of the former that contain abnormal 

 vascular bundles. Monocotyledonous roots and rhizomes do 

 not possess medullary rays, whilst in most dicotyledonous 

 roots and rhizomes they are present and may be found in the 

 powdered drugs in fragments, exhibiting typical appearances 

 according as they present their transverse, tangential or radial 

 section. 



In some few cases it is possible to distinguish an admixture 

 of powdered rhizome with powdered root, but generally speaking 

 this is difficult, if not impossible. Gentian or liquorice rhi- 

 zome, for instance, cannot be distinguished from the root when 

 powdered, but an admixture of ipecacuanha or valerian rhizome 

 with the root can easily be detected, as the rhizomes contain 

 certain sclerenchymatous elements which are not found in the 

 roots. 



The following are the principal tissues that may be found in 

 powdered roots or rhizomes : epidermis or cork,%)helloderm, collen- 

 hyma, cortical parenchyma, endodermis, bast, wood, and pith. 

 They are not, however, all of the same diagnostic importance ; 

 thus, for instance, the phelloderm and collenchyma are almost 

 valueless from a diagnostic point of view, whereas sclerenchy- 

 matous cells, fibres, etc., are extremely important, as are also 

 5-uch cell contents as stnrch, iniiliw, calcium oxalatc, etc. 



