COMPARED WITH THOSE OF ANIMALS. 



67 



crystals are of different sizes and forms, rhomboidal, cubi- 

 cal, and prismatic ; but the most prevalent figure is the 

 acicular and needle-shaped. They occur either singly or 

 in stellate masses. The stellate figure is generally assumed 

 by the acicular and prismatic varieties, to which the term 

 raphides (ports'* a needle,) was originally applied by Decan- 

 dolle, although it is now used indiscriminately in reference 

 to all cellular crystals. These crystals occur in all parts of 

 the plant, in the stem, bark, leaves, petals, and root ; they 

 usually consist of the oxalic, carbonic, malic, phosphoric, 

 citric, and other organic acids united to lime as a base. 

 The octohedral variety may be readily seen in the cuticular 

 cells of the bulb of the onion. Acicular crystals may be 

 procured from the petiole of Calla Ethiopica, by making a 

 section and spreading the mucilaginous contents of the 

 cells over the field of the microscope. 



The adipose tissue of old persons sometimes contains 

 acicular crystals. Fat consists of a liquid and solid prin- 

 ciple, the former is termed elaine, the latter margarine. 

 These acicular crystals are the solid element or margarine 

 which has separated from the elaine. 



Fig. 17. 





Adipose cells, each containing needle-shaped crystals of margarine. 



