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. 
16. 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- 
