CELL-CONTENTS AND FORMS OF CELLS. 189 



VIL Membrane Crystals.— There are several forms of 

 crystals which may be included in this group. The so-called 

 Rosanoff crystals consist of rosette aggregates attached to inward- 

 protruding walls of the plant cell. These, however, do not concern 

 us so much as the large monoclinic crystals which have a mem 

 brane surrounding them. The crystal first appears in the cell-sap, 

 and then numerous oil globules appear in the protoplasm around 

 it; later some of the walls of the cell thicken and grow around 

 the crystal, which they finally completely envelop, as in Morace^e. 



Crystals of the orthorhombic system may occur either as soli- 

 tary crystals or rosette aggregates, or in the form of acicular 

 crystals and probably micro-crystals, being usually much smaller 

 than the single crystals of the monoclinic system. 



Solereder, in his work on " Systematic Anatomy of the Dicoty- 

 ledons,"' states that the systematic value of the study of the forms of 

 crystals varies considerably. While in some instances a certain 

 form of crystal is characteristic of an entire order, yet in other 

 cases it serves to distinguish only genera or species. In practical 

 work in the identification of economic products the study of the 

 forms of crystals is very important. A few instances may be 

 mentioned. In Jamaica quassia calcium oxalate occurs in the 

 form of 4- to 6-sided rhombohedral crystals, whereas in Surinam 

 quassia the crystals are few or entirely wanting. In Levant 

 scammony root occur numerous monoclinic prisms of calcium oxa- 

 late, whereas in the Mexican root the crystals are chiefly in the 

 form of rosette aggregates. In the bark of Viburnum Opulus the 

 calcium oxalate occurs almost entirely in the form of rosette aggre- 

 gates, whereas in the bark of Acer spicatuui solitary rhombo- 

 hedral crystals are prevalent. In the identification of many 

 drugs the presence or absence of calcium oxalate crystals and 

 the study of the prevalent forms is very important (Fig. no). 



Owing to the importance of the study of calcium oxalate an 

 enumeration of the families in which calcium oxalate occurs is 

 given. 



I. Crystals of calcium oxalate, either in the form of solitary 

 rhombohedra or clustered aggregates, are found in the following 

 families: Aceracese, Ampelidacese (also raphides), Anacardiace^e, 

 Apocynacese, Araliacese, Asclepiadaceae, Berberidaceae, Bignonia- 



