92 HISTOLOGY OF MEDICINAL PLANTS 



Crystal-bearing fibres occur in the barks of frangula (Plate 

 19, Fig. i); cascara sagrada (Plate 19, Fig. 2); witch-hazel 

 (Plate 19, Fig. 4); in cocillana (Plate 20, Fig. i); in white oak 

 (Plate 20, Fig. 2); in quebracho (Plate 20, Fig. 3); and in 

 Spanish licorice root (Plate 19, Fig. 3). 



The crystal-bearing fibres of leaves are always associated 

 with vessels or tracheids and with cells with chlorophyl. The 

 presence or absence of crystal-bearing fibres in leaves should 

 always be noted. The crystal-bearing fibres of leaves are 

 composed of fragments of conducting cells, fibres, crystal cells, 

 and crystals. The crystal-bearing fibres of leaves occur in 

 larger fragments than the other parts of the leaf, because the 

 fibres are more resistant to powdering. Having observed that 

 a leaf has crystal-bearing fibres, in order to identify the powder 

 it is necessary to locate one of the other diagnostic elements 

 of the leaf — as the papillae of coca (Plate 21, Fig. i), or the hair 

 of senna (Plate 2 1 , Fig. 3) , or the vessels in eucalyptus (Plate 2 1 , 

 Fig. 2). 



Branched bast fibres occur in only a few of the medicinal 

 plants, notable examples being tonga root and sassafras root. 

 Occasionally one is found in mezereum bark. 



The bast fibre of tonga root (Plate 22, Fig. 2) often has seven 

 branches, but four- and five-branched forms are more common. 

 The walls are non-porous, non-striated, and nearly white. 



The bast fibre of sassafras (Plate 22, Fig. i) has thick, non- 

 porous, and non-striated walls, and the branching occurs usually 

 at one end only of the fibre. Most of the bast fibres of sassafras 

 root are non-branched. 



POROUS AND STRIATED BAST FIBRES 



Porous and striated walled bast fibres occur in blackberry 

 bark of root, wild-cherry bark, and in cinchona bark. 



The fibres of blackberry root bark (Plate 23, Fig. i) have 

 distinctly porous and striated walls; the cavity, which is usually 

 greater than the diameter of the wall, contains starch. These 

 fibres usually occur as fragments. 



In wild-cherry bark (Plate 23, Fig. 2) the fibre has short, 

 thick, unequally thickened walls, which are porous and striated. 

 Most of the fibres are unbroken. 



