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, 

 and as a T. 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 parench^ona 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- 



