THE INTERNAL STRUCTURES OF PLANTS. 



211 



become distended so as to burst, and force out the con- 

 tents, as here shown. Cells with similar contents are 

 also found in the leaves of four-o'clock, Indian tur- 

 nip, and calla. These cell-crystals are sometimes ag- 

 glomerated into masses of angular crystals (Fig. 382). 



FIG. 882. 



That these crystal are formed in the cells is proved 

 by the fact that the shape of the cell determines the 

 form of the crystal. SUea, the substance known every- 

 where as sand, exists, dissolved, in the sap of plants, 

 and is deposited in the stalk of grains in such quanti- 

 ties as to give them the requisite stiffness. 



