200 HISTOLOGY OF MEDICINAL PLANTS 
CRYSTALS 
Calcium oxalate crystals form one of the most important 
inorganic cell contents found in plants, because of the per- 
manency of the crystals, and because the forms common to 
a given species are invariable: By means of calcium oxalate 
crystals it is possible to distinguish between different species. 
In butternut root bark, for instance, only rosette crystals are 
found, while in black walnut root bark—a common substitute 
for butternut bark—both prisms and rosettes occur. This is 
only one of the many examples which could be cited. 
These crystals, for purposes of study, will be grouped into 
four principal classes, depending upon form and not upon crystal 
system. These classes are micro-crystals, raphides, rosettes, 
and solitary crystals. 
MICRO-CRYSTALS 
Micro-crystals are the smallest of all the crystals. Under the 
high power of the microscope they appear as a V, a Y, an X, 
andasaT. They are, therefore, three- or four-angled (Plate 78). 
The thicker portions of these crystals are the parts usually 
seen, but when a close observation of the crystals is made the 
thin portions of the crystal connecting the thicker parts may 
also be observed. Micro-crystals should be studied with the 
diaphragm of the microscope nearly closed and with the high- 
power objective in position. While observing the micro-crystals, 
raise and lower the objective by the fine adjustment in order to 
bring out the structure of the crystal more clearly. Micro- 
crystals occur in parenchyma cells of belladonna, scopola, 
stramonium, and bittersweet leaves; in belladonna, in horse- 
nettle root, in scopola rhizome, in bittersweet stems, and in 
yellow and red cinchona bark, etc. 
The crystals in each of the above parts of the plant are similar 
in form, the only observed variation being that of size. Their 
presence or absence should always be noted when studying 
powders. 
RAPHIDES 
Raphides, which are usually seen in longitudinal view, re- 
semble double-pointed needles. They are circular in cross- 
