196 HISTOLOGY or 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. i). 



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 A 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. 



