92 : HISTOLOGY OF MEDICINAL PLANTS 
Crystal-bearing fibres occur in the barks of frangula (Plate 
19, Fig. 1); cascara sagrada (Plate 19, Fig. 2); witch-hazel 
(Plate 19, Fig. 4); in cocillana (Plate 20, Fig. 1); 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 papille of coca (Plate 21, Fig. 1), or the hair 
of senna (Plate 21, Fig. 3), or the vessels in eucalyptus (Plate 21, 
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. 1) 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. 1) 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. 
