60 



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

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



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. 59, 

 60, and 61, the crystalforms of turmaline 

 (C V 3 ), of silver-iodide: AgJ (C^), and 

 of struvite: Mg(NH^)PO^ + 6# 2 O (C v 2 ) t 

 are reproduced. 



In all these figures the prominent 

 feature of the hemimorphic develop- 

 ment is immediately seen; indeed, this 

 peculiarity of their external shape is 

 one of the most characteristic of 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 reproduce in fig. 62 two 

 objects which manifest this symmetry 

 very strikingly: the fruit of Bignonia 

 echinata (Gaertner) shows the sym- 

 metry of group C V 2 . 



The blossoms of many Cruci 'ferae, of 



Circaea lutetiana, of Fraxinus, etc., evidently belong to the same class. 



In the domain of ani- 

 mal life we can mention 



as representatives of this 



symmetry, a number of 



Ascidiae: Polydinum con- 



stellatum; of Radiolaries: 



Spyridibotrys trinacria. 



The polar nature of the 



principal axis of all these 



objects will be clearly 



noticed in the examples 



chosen. 



Of the group C V 3 we 



reproduce in fig. 6j the fruit of Gloriosa superba, in fig. 64. that 



of Canarium decumanum. Also the blossoms of Camphor a of fid- 



Fig. 62. 



Fruit of 

 Bignonia echinata. 



Fig. 63. 

 Fruit of Gloriosa superba. 



