210 HISTOLOGY OF MEDICINAL PLANTS 
tamarac (Plate 85), quassia, uva-ursi, quebracho, and in wild 
cherry (Plate 86). 
The crystals of morea nutgalls (Plate 82, Fig. 3) are octo- 
hedrons, and they resemble the crystals of calcium oxalate found 
in urinary sediments. 
While studying the prisms, focus first on the upper surface 
and then down to the under surface in order to observe the 
forms accurately. 
There are several plants in which more than one form of 
crystal occur. Rosette crystals and prisms are associated, for 
instance, in cascara sagrada, frangula, condurango, dogwood, 
and pleurisy root (Plate 87, Figs. 1, 2, 3, 4, and 5). 
An important factor to be kept in mind in studying crystals 
is the number—whether abundant, as in rhubarb, or sparingly 
present, as in mandrake, etc. Variation in the number of 
crystals is not uncommon, even in different parts of the same 
plants. In wahoo stem bark, for ‘instance, there are several 
times as many rosette crystals as there are in the root bark. 
Crystals of calcium oxalate are freely soluble in dilute 
hydrochloric acid without effervescence; but they are insoluble 
in acetic acid and in sodium and potassium hydroxide solutions. 
With sulphuric acid they form crystals of calcium sulphate. 
CYSTOLITHS 
Cystoliths consist of calcium carbonate deposited over and 
around a framework of cellulose. 
FORMS OF CYSTOLITHS 
The forms of cystoliths differ greatly in the different plants 
in which they occur. 
In the rubber-plant leaf, the cystolith resembles a bunch of 
grapes and is stalked; in ruellia root (Plate 87, Fig. 1) the cysto- 
liths vary from nearly circular to narrowly cylindrical, and no 
stalk is present; also the cystolith nearly fills the cell in which 
it occurs. In the hair of cannabis indica (Plate 88, Fig. 3), the 
cystolith varies in form according to the size and shape of the 
hair, but in all the hairs the cystolith appears to be attached to 
the upper curved part of the inner wall of the hair. 
