196 HISTOLOGY OF MEDICINAL PLANTS 
drugs the mucilage masses are mostly spherical or oval in outline 
(Plate 66, Figs. 2 and 3) the form being similar to the cavity 
in which the mass occurs. 
Acacia, tragacanth, and India gum consist of the dried 
mucilaginous excretions. 
HESPERIDIN 
Hesperidin occurs in the epidermal cells of short and long 
buchu. It is particularly characteristic in the epidermal cells 
of the dried leaves of short buchu. In these leaves the hesperidin 
occurs in masses which resemble rosette crystals (Plate 54, Fig. 1). 
Hesperidin is insoluble in glycerine, alcohol, and water, but 
it dissolves in alkali hydroxides, forming a yellowish solution. 
VOLATILE OILS 
Volatile oils occur in cinnamon stem bark, sassafras root 
bark, flowers of cloves, and in the fruits of allspice, anise, fennel, 
' caraway, coriander, and cumin. 
In none of these cases is the volatile oil diagnostic, but its 
presence must always be determined. 
- When a powdered drug containing 4 volatile oil is placed 
in alcohol, glycerine, and water mixture the volatile oil con- 
tained in the tissues will accumulate at the broken end of the 
cells in the form of rounded globules, while the volatile oil 
adhering to the surface of the fragments will dissolve in the 
mixture and float in the solution near the under side of the 
cover glass. Volatile oil is of little importance in histological 
work. 
TANNIN 
Tannin masses are usually red or reddish brown. Tannin 
occurs in cork cells, medullary rays of white pine bark (Plate 48, 
Fig. B), stone cells, and in special tannin sacs. 
The stone cells of hemlock and tamarac bark and the medul- 
lary rays of white pine and hemlock bark contain tannin. 
Tannin associated with prisms occurs in tannin sacs in white 
pine and tamarac bark. These sacs are frequently several 
millimeters in length and contain a great number of crystals 
surrounded by tannin. 
