CRYSTALS IN PLANTS. 



339 



crystals will be principally prismatic, and are arranged as 

 if they were beginning to assume a stellate form. Some 

 plants, as many of the cactus 

 tribe, are made np almost 

 entirely of raphides. In 

 some instances every cell of ^ 

 the cuticle contains a stel- 

 late mass of crystals ; in 

 others the whole interior is 

 full of them, renderino; the 

 plant so exceedingly brittle, 

 that the least touch will 

 occasion a fracture; so much 

 so, that some specimens of 

 Cactus senilis, said to be a 

 thousand years old, which 

 were sent a few years since 

 to Kew from South America, 

 were obliged to be packed 

 in cotton, with all the care 

 of the most delicate jewel- 

 lery, to preserve them during transport. 



Raphides, of peculiar figure, are common in the bark of 

 many trees. In the Hiccory 



Fig. 184. — Siliceous cuticle from under 

 surface of leaf of Deutzia scabra. 



v^^J' 





'T^ 



J^ 







%i\ 





l^ ^ 



^ 





{Carya alba) may be ob- 

 served masses of flattened 

 prisms having both extre- 

 mities pointed. In vertical 

 sections from the stem of 

 Eloeagiius angustifolia, nu- 

 merous raphides of large size 



are embedded in the" pith. ^^W ^ ^ "^'"^ tW 

 Raphides are also found in ^f ^5^ j4. "" ^'^'Fl 



the bark of the apple-tree, ^ |-jO '^ ^ ^ O 

 and in the testa of the seeds t^ f ~jr-^ 3V -^J^ 

 of the elm ; every cell con- ^ r in^ VW >^f ")) 

 tains two or more very .^z: rn"^ '^ ^"^ )>r^ 

 minute crystals. ^1 j k "^ >^V r'k 



In figs. 184 and 185 we ''^-^- ^ ^ ^^ lf-& 

 have other representations Fig. i^^.—siUceous cuticle of Grass 

 of the crystalline structure ^^^«^«' ^'•"''''«») 



z 2 



'f^ 



