58 



our systematical deduction of the other groups of the second order. 

 The symmetry of the type C% plays a very important role in nature, 



Fig. 58. 



Silver-iodide. 



Fig. 59- 



Struvite. 



and more particularly among living beings; but there are also many 

 representatives of it known among the forms of crystalline matter. 



As instances of this kind, in fig.J>7,5&, 

 and 59, the crystal-forms of turmaline 

 (C V s), of silver-iodide: AgJ (C^), and of 

 struvite: Mg(NH^)PO^6H 2 (C/), are 

 reproduced here. 



In all these figures the prominent 

 feature of the hemimorphic development 

 is immediately seen ; indeed, this pecu- 

 liarity of their external shape is one 

 of the most characteristic things about 

 crystals of this kind, just as in the 

 cases of C n . 



In living nature, the type of sym- 

 metry mentioned is one of those most 

 frequently occurring. As instances in 

 botany, we have reproduced here in 

 fig. 60 some fruits and flower-diagrams 

 which manifest this symmetry very 

 strikingly indeed. So in fig. 60 there is 

 reproduced a fruit of Bignonia echinata. 

 (Gaertner), which shows the symmetry of group C V 2 . 



Fig. 60. 

 Fruit of 



Bignonia echinata. 



