VEGETABLE CYTOLOGY 87 



4. Raphides Convallaria, Sarsaparilla, Veratrum, -Scilla, 

 Phytolacca. 



5. Micro-crystals (Crystal sand) Bellandonnae Radix, Cinchona, 

 Stramonium, Phytolacca, Capsicum. 



6. Crystal Fibers Cascara Sagrada, Prunus Virginiana, Gly- 

 cyrrhiza, Aspidosperma. 



7. Membrane Crystals Aurantii Dulcis Cortex, Limonis Cortex, 

 Condurango. 



Solitary crystals, usually in the form of rhombohedra, occasionally 

 in twin crystals, occur as sharp angular bodies, each one often com- 

 pletely filling up the lumen of a cell. 



Rosette aggregates consist of numerous small prisms or pyramids, 

 or hemihedral crystals arranged around a central axis, appearing 

 like a rosette or star. 



Columnar crystals or styloids are elongated prisms. 



Raphides are groups of acicular or needle-shaped crystals, which 

 occur in long thin-walled cells containing mucilage. They are 

 more frequently found in Monocotyledons than in any other plant 

 group. Micro-crystals (sphenoidal micro-crystals or crystal sand) 

 are minute arrow-shaped or deltoid forms completely filling the 

 parenchyma cells in which they occur and giving these a grayish- 

 black appearance. 



Crystal fibers are longitudinal rows of superimposed parenchyma 

 cells each of which contains a single monoclinic prism or rosette 

 aggregate. Crystal fibers are found adjacent to sclerenchyma fibers 

 such as bast or woody fibers. 



Membrane crystals are monoclinic prisms, each of which is sur- 

 rounded by a wall or membrane. In the process of formation a 

 crystal first is formed in the cell sap and then numerous oil globules 

 make their appearance in the protoplasm surrounding it; later some 

 of the walls of the cell grow around the crystal and completely 

 envelop it. 



1 6. Cystoliths. Cystoliths are clustered bodies formed by the 

 thickening of the cell wall at a certain point and subsequent in- 

 growth which latter forms a cellulose skeleton consisting of a stalk 

 and body. Silica is subsequently deposited on the stalk while 

 calcium carbonate is piled up on the body in layers, forming an irregu- 



