TISSVB. 



87 



cells, and lie parallel in bundles. Still other forms are 

 prisms, octohedra, etc. They may be either simple (.Figs. 



196, 197), or compound (Fig. 198). Crystals of calcic 

 carbonate are not so common. A peculiar form, called 

 cystoliths (Gr. cystis, bladder ; lithos, stone), occurs in the 

 leaves of the TJrticacece (Nettle, Fig^ Mulberry, Hop, etc.), 

 a club-shaped outgrowth of cellulose projects into the cell, 

 and in this multitudes of small crystals are grouped (Fig. 

 199). It is said that crystals of calcic phosphate, calcic 

 sulphate, and silica, are occasionally to be met with. It 

 is probable that crystals are residual products of chemical 

 action in the plants, and are, therefore, to be regarded as 

 of the nature of excretions. 



TISSUE. 

 112. Some of the lower plants consist of but a single 

 cell, and are, therefore, called uni- 

 cellular plants. Such are the Pr-o- 

 tococeus, Desmids, Bacteria, etc. 

 Many of the unicellular plants 

 are more or less bound together 

 by a jelly-like substance, and thus 

 form cell-colonies, as in Gleocapsa "s 



Figs. 196-198. Crystals in cells: 196. Raphides ; 196,197. Simple crystals; 198. 

 Compound crystal. Fig. 199. A cystolith in a Nettle leaf. 



■AkJO 



