46 



try-classes: to group T those of Corydalis sempervirens; and 

 of group P, the pollen-cells of Buchholzia maritima, Fumaria 

 spicata, Polygonum amphibium, Rivina brasiliensis, Bannisteria 

 versicolor, etc. The number of these examples can certainly be 

 augmented. Some of these pollen-cells are reproduced in fig. 49. 

 11. As has been repeatedly stated, all forms and objects 

 which show the symmetry of any of these groups possessing only 



axes of the first 

 order, are diffe- 

 rent from their 

 mirror-images. Of 

 course all these 



stereometrical 

 figures and ob- 

 jects lack an 

 inversion-centre, 

 or, as is commonly 

 said, they do not 

 possess a sym- 

 metry-centre l ). 

 This is a fact 

 which is of im- 

 portance with 

 respect to some 

 physical proper- 

 ties, e. g., hi the 

 case of crystals, as will be demonstrated more in detail later on 



This fact of the occurrence 

 of two different forms 

 for every symmetrical ob- 

 ject of this kind, which 

 bear upon each other as 

 mirror-images, is known as 

 enantiomorphism; and both 

 possible forms are called 



Fig. 49. 

 Pollen-cells of 



Dianthus Cartusianorum (1). Luzula campestris (4). 

 Circaea alpina (2). Mastixea arborea (5). 



Rivina humilis L. (3). 



enantiomorphous. 

 The phenomenon of enan- 



Fig. 50. 



Right-, and left-handed 

 deltoid-dodecahedron . 



1) It may be remarked that the reverse of this conclusion is not generally 

 true: from the absence of a symmetry-centre, enantiomorphism does not 

 follow necessarily. 



