Crystals 



n 



Raphides or Crystals.— Very often some of the mineral 

 substances contained in the sap become crystallised out, and 

 make their appearance either within the cdl or in the wall. In 

 some plants the amount of these crystals is very great. In the 

 Old-Man Cactus, as much as 80 per cent, of the dried tissue 

 consists of them. Professor Bailey found in a square inch of 

 Locust bark no thicker than writing paper, as many as a million 

 and a half of these crystals. The root of Turkey Rhubarb 

 contains so many as to give a gritty character to it when chewed. 

 As a rule the raphides are found in cells where there are no 



Fig. 13.— Cell from the stem of 

 Aloe rehisa, with raphides. 



Fig. 14.— Crystalloid, kr^ in a 

 parenchymatous cell of the 

 Potato tuber ; k^ nucleus. 



other granular contents, but this is not universal. In chemical 

 composition they consist of phosphate of calcium, or more 

 often of oxalate of calcium. Carbonate or sulphate of calcium 

 is sometimes met with. In shape they are either cubical, octo- 

 hedral, or needle-like (hence the name of raphides, from the 

 Greek name for a needle). 



Crystalloids. — In some cells, especially those of fatty seeds 

 like the Brazil nut, bodies are found which are crystal-like in 

 appearance, but instead of being mineral in composition, con- 

 sist of proteinaceous or nitrogenous material closely allied to 



