NON-PROTOPLASMIC CELL CONTENTS 91 
12. Micro-crysrats (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. While sometimes classified with 
the calcium oxalate crystals, they are thought to represent some 
other compound as yet undetermined. 
13. Cysro.irus.—Cystoliths are clustered bodies formed by 
the thickening of the cell wall at a certain point and subsequent 
ingrowth 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, form- 
ing an irregular spheroidal or ellipsoidal deposit. ‘These struc- 
tures are abundantly found in the plants of the Nettle, Mulberry 
and Acanthus families and constitute a leading peculiarity of the 
same (see Fig. 52). They also occur in the Combretum and 
Borage families, in species of Phlox, Klugia, etc. ‘They are proba- 
bly excretory products. Excellent materials for the study of 
cystoliths are the leaves of the rubber plant (Ficus elastica) and 
the fig (F. carica). Here, the cystoliths appear as stalked 
mulberry-like structures suspended from the outer walls of 
specialized epidermal cells called “‘cystolith sacs.” 
Hair cystoliths differ from the average type in that they are 
devoid of a stalk. Such are seen in the non-glandular hairs of 
Cannabis sativa. 
The calcium carbonate incrustation of a cystolith dissolves 
with effervescence on the addition of a mineral or organic acid. 
14. Smica.—Silica (SiO,) occurs in a number of plants 
either as an incrustation in the cell wall, as in Diatoms, the 
Equisetinee and Gramineae or more rarely in the form of “silica 
bodies,” such as are found in certain Palms and Orchids. It is 
insoluble in» all the acids except hydrofluoric. It may be 
obtained in pure form by placing tissue containing it in a drop or 
two of concentrated sulfuric acid and after a time treating with 
successively stronger solutions of chromic acid (starting with 25 
per cent.) and then washing with water and alcohol. 
In a number of members of the Palme, Orchidacea, 
Scitaminea, etc. the strands of sclerenchyma fibers are accom- 
panied by rows of small, tongue-shaped cells called stegmata. 
