192 BARKS. 



(94) Cinchona Bark (Ledger). 



The cultivated bark of Cinchona Ledgeriana, Moens (N.O. 

 Rubiacese). 



The bark presents the following structure : 



(1) Cork, composed of several layers of thin-walled tabular 

 cells filled with a dark-brown, amorphous substance ; in surface 

 view the cells are polygonal. 



(2) Phelloderm, consisting of several rows of cells with dark- 

 brown walls. 



(3) Cortex, composed of tangentially elongated polygonal 

 cells, some of which are filled with sandy crystals of calcium 

 oxalate, while others contain small, simple starch grains. 



(4) Bast Ring, comprising the major part of the bark. The 

 medullary rays traversing this tissue are usually two or three 

 cells wide, and the cells have very thin walls. The bast-rays 

 contain numerous scattered bast-fibres which vary somewhat 

 in width (30 to 80 /*), but are usually rather large and fusiform 

 in shape ; their walls are very thick, conspicuously striated, and 

 traversed by funnel-shaped pits. In the powdered drug the 

 bast fibres are more or less broken, but the fragments are easily 

 recognisable by their characteristic pits. The sieve-tubes are 

 very narrow, and the sieve-plates are usually transversely 

 situated. 



The powder of cultivated cinchonas always contains frag- 

 ments of very dark-brown cork and of foliaceous lichens ; they 

 usually exhibit but few sclerenchymatous cells, but the 

 botanical source cannot be accurately determined by means of 

 the microscope. 



The diagnostic characters of powdered cinchona bark are : 



(a) The dark colour of the parenchy matous tissue. 



(b) The very characteristic bast fibres. 



(c) The small sieve-tubes. 



