356 RUBIACE^. 



this is the case are therefore at last exclusively composed of liber, of 

 which Flat Calisaya Bark is a good example. 



The liber is traversed by medullary rays, which in cinchona are 

 mostly very obvious, and project more or less distinctly into the middle 

 cortical tissue. The liber is separated by the medullary rays into 

 wedges,^ which are constituted of a parenchymatous part and of yellow 

 or orange fibres. The number, colour, shape, and size, but chiefly the 

 arrangement of these fibres, confer a certain character common to all the 

 barks of the group under consideration. 



The liber-fibres ^ are elongated and bluntly pointed at their ends, but 

 never branched, mostly spindle-shaped, straight or slightly curved, and 

 not exceeding in length 3 millimetres. They are consequently of a 

 simpler structure than the analogous cells of most other officinal barks. 

 They are about ^ to ^ mm. thick, their transverse section exhibiting a 

 quadrangular rather than a circular outline. Their walls are strongly 

 thickened by numerous secondary deposits, the cavity being reduced to 

 a narrow cleft, a structure which explains the brittleness of the fibres. 

 The liber-fibres are either irregularly scattered in the liber-rays, or the}' 

 form radial lines transversely intersected by narrow strips of paren- 

 chyme, or they are densely packed in short bundles. It is a peculiarity 

 of cinchona barks that these bundles consist always of a few fibres (3 

 to 5 or 7), whereas in many other barks (as cinnamon) analogous 

 bundles are made up of a large number of fibres. Barks provided with 

 long bundles of the latter kind acquii'c therefrom a very fibrous fracture, 

 whilst cinchona barks from their short and simple fibres exhibit a short 

 fracture. It is rather granular in Calisaya bark, in which the fibres are 

 almost isolated by parenchymatous tissue. In the bark of C. scro- 

 hiculata, a somewhat short fibrous fracture * is due to the arrangement 

 of the fibres in radial rows. In C. pubescens, the fibres are in short 

 bundles and produce a rather woody fracture. 



Besides the liber-fibres, there are some other cells contributing to 

 the peculiarity of individual cinchona barks. This applies chiefly 

 to the laticiferous ducts or vessels'^ which are found in many sorts ; 

 they are scattered through the tissue intervening between the middle 

 cortical layer and the liber, and consist of soft, elongated, unbranched 

 cells, mostly exceeding in diameter the neighbouring parenchymatous 

 cells. 



As to the contents of the tissue of cinchona barks, crystallized 

 alkaloids are not visible, Howard has published figures representing 

 minute rounded aggregations of crystalline matter in the cells, which 

 he supposes to be kinovates of the alkaloids ; and also distinct acicular 

 crystals which he holds to be of the same nature. These remarkable 

 appearances are easily observiable, yet only after sections of the bark 

 have been boiled for a minute in weak caustic alkali and then washed 

 with water ; it may well be doubted whether they are strictly natural. 

 The liquids which are capable of dissolving the alkaloids in the free 

 state do not afibrd any if they are applied to the barks. The alkaloids 

 being contained in the bark in the form of salts, the latter are decom- 



^ Baststrahlen or Phloemstrahlen of the ^ Fracture filandreuse, Weddel ; fadiger 



Germans. Bruch of the Germans, 



^ Fibres corticales of Weddell ; Bastrohren * Vaisseaux latki/ires of Weddell ; Milch 



or Bastzellen in German. saftscldduche in German. 



i 



