250 RHIZOMES AND BOOTS. 



(120) Orris Rhizome. 



The rhizome of Iris florentina, etc. (N.O. Iridese). 

 The rhizome presents the following structure : 



(1) Cork, consisting of numerous layers of thin-walled cork 

 cells, followed by 



(2) Collenchyma, of which there are several rows. Both of 

 these tissues are, however, removed from the rhizome by peeling 

 before it is sent into commerce. The outermost layer of the 

 commercial drug is therefore 



(3) Cortex, part of which is also usually removed by the peel- 

 ing; the cells are irregularly polygonal in shape and exhibit 

 intercellular spaces ; the walls are thickened and conspicuously 

 pitted. 



(4) Endodermis, the cells of which are tangentially elongated. 



(5) Stele, composed largely of parenchymatous tissue, re- 

 sembling that of the cortex, traversed by numerous concentric 

 fibre-vascular bundles, which are closely approximated near the 

 endodermis. 



The parenchymatous cells, both of the cortex and the stele, are 

 filled with starch grains of very characteristic appearance. 

 They are mostly simple and vary from 25 to 50/x, in length, and 

 from 10 to 25/i in width. Many are elongated, oval or elliptical 

 in outline, or rounded at one extremity and flat at the other ; 

 sometimes slightly curved or with irregular protuberances. The 

 hilum is distinct, eccentric and stellate or branching. Here 

 and there compound grains are met with. 



Conspicuous also in both cortex and stele are very large 

 prismatic crystals of calcium oxalate. These crystals attain a 

 length of 250ju, and a width of 30ju. They occur in intercellular 

 spaces and are enclosed in suberised membranes. Sometimes 

 more than one crystal may be found in the same intercellular 

 space. 



The diagnostic characters of orris rhizome are : 



(a) The starch grains. 



(b) The large prismatic crystals. 



(c) The thick-walled parenchymatous cells. 



(d) The absence of sclerenchymatous cells or fibres. 



