172 PLANT ORGANS OR PARTS OF PLANTS. 



become markedly wider toward the periphery. The 

 medullary rays contain starch and oil cells. Oil cells and 

 crystal sacs are to be found in the inner bark also. 



Histology. — The periderm is composed of thin- walled 

 cork cells with here and there groups with walls some- 

 what thickened. The outer portion of the cortical 

 parenchyma is composed of rectangular cells in regular 

 radial files surrounding small and large groups of tan- 

 gentially elongated stone cells. In the looser and more 

 irregular layer of larger polygonal cells within are distrib- 

 uted numerous large oil or resin cells with yellow con- 

 tents and still more numerous groups of calcium oxalate 

 raphides with more rarely single cubical crystals. The 

 inner bark with its long well-developed phloem bundles 

 occupies three-fourths of the thickness of the bark. 

 These phloem bundles of layers of regular bast paren- 

 chyma, thick- walled where inclosing sieve tube groups, 

 with here and there groups of small thick-walled bast 

 fibres, make up the laminated portion of the bark. The 

 medullary rays, two and three cells wide, expanding 

 outwardly, contain much starch, as does also the bast 

 parenchyma. Here, as in the outer bark, calcium 

 oxalate crystals and oil cells are frequent. 



The Powder. — The elements of the powder are the large 

 oval oil or resin cells, surrounded by smaller-celled thin- 

 walled parenchyma, calcium oxalate, rarely in rhom- 

 boidal crystals, starch grains, cork cells, sometimes some- 

 what thickened on the outer side, and occasionally narrow 

 thick- walled bast fibres with simple pointed ends. Nu- 

 merous groups of irregular thick-walled phloem paren- 

 chyma representing the sieve tube portion of the liber 

 are also met with. None of these elements, except per- 

 haps the oil cells, are by themselves particularly character- 

 istic, but altogether they render the recognition of the 

 powder a matter of no great difficulty. 



Substitutes and Adulterants.— False Angostura, the 



